From 064d9262332461dfd7bda4e763a3e724777a831d Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Sun, 18 Feb 2024 21:53:15 +0100
Subject: [PATCH] Initial commit

---
 LICENSE                     | 661 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 README.md                   |   9 +++++++++
 db.go                       | 200 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 entity.go                   | 250 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 go.mod                      |   9 +++++++++
 go.sum                      |   6 ++++++
 main.go                     | 451 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 middleware.go               |  82 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 schema.sql                  |  38 ++++++++++++++++++++++++++++++++++++++
 static/style.css            |   9 +++++++++
 template/authorize.html     |  15 +++++++++++++++
 template/client-secret.html |  16 ++++++++++++++++
 template/foot.html          |   2 ++
 template/head.html          |   9 +++++++++
 template/index.html         |  24 ++++++++++++++++++++++++
 template/login.html         |  15 +++++++++++++++

diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000000000000000000000000000000000000..0ad25db4bd1d86c452db3f9602ccdbe172438f52
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,661 @@
+                    GNU AFFERO GENERAL PUBLIC LICENSE
+                       Version 3, 19 November 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The GNU Affero General Public License is a free, copyleft license for
+software and other kinds of works, specifically designed to ensure
+cooperation with the community in the case of network server software.
+
+  The licenses for most software and other practical works are designed
+to take away your freedom to share and change the works.  By contrast,
+our General Public Licenses are intended to guarantee your freedom to
+share and change all versions of a program--to make sure it remains free
+software for all its users.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+them if you wish), that you receive source code or can get it if you
+want it, that you can change the software or use pieces of it in new
+free programs, and that you know you can do these things.
+
+  Developers that use our General Public Licenses protect your rights
+with two steps: (1) assert copyright on the software, and (2) offer
+you this License which gives you legal permission to copy, distribute
+and/or modify the software.
+
+  A secondary benefit of defending all users' freedom is that
+improvements made in alternate versions of the program, if they
+receive widespread use, become available for other developers to
+incorporate.  Many developers of free software are heartened and
+encouraged by the resulting cooperation.  However, in the case of
+software used on network servers, this result may fail to come about.
+The GNU General Public License permits making a modified version and
+letting the public access it on a server without ever releasing its
+source code to the public.
+
+  The GNU Affero General Public License is designed specifically to
+ensure that, in such cases, the modified source code becomes available
+to the community.  It requires the operator of a network server to
+provide the source code of the modified version running there to the
+users of that server.  Therefore, public use of a modified version, on
+a publicly accessible server, gives the public access to the source
+code of the modified version.
+
+  An older license, called the Affero General Public License and
+published by Affero, was designed to accomplish similar goals.  This is
+a different license, not a version of the Affero GPL, but Affero has
+released a new version of the Affero GPL which permits relicensing under
+this license.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+                       TERMS AND CONDITIONS
+
+  0. Definitions.
+
+  "This License" refers to version 3 of the GNU Affero General Public License.
+
+  "Copyright" also means copyright-like laws that apply to other kinds of
+works, such as semiconductor masks.
+
+  "The Program" refers to any copyrightable work licensed under this
+License.  Each licensee is addressed as "you".  "Licensees" and
+"recipients" may be individuals or organizations.
+
+  To "modify" a work means to copy from or adapt all or part of the work
+in a fashion requiring copyright permission, other than the making of an
+exact copy.  The resulting work is called a "modified version" of the
+earlier work or a work "based on" the earlier work.
+
+  A "covered work" means either the unmodified Program or a work based
+on the Program.
+
+  To "propagate" a work means to do anything with it that, without
+permission, would make you directly or secondarily liable for
+infringement under applicable copyright law, except executing it on a
+computer or modifying a private copy.  Propagation includes copying,
+distribution (with or without modification), making available to the
+public, and in some countries other activities as well.
+
+  To "convey" a work means any kind of propagation that enables other
+parties to make or receive copies.  Mere interaction with a user through
+a computer network, with no transfer of a copy, is not conveying.
+
+  An interactive user interface displays "Appropriate Legal Notices"
+to the extent that it includes a convenient and prominently visible
+feature that (1) displays an appropriate copyright notice, and (2)
+tells the user that there is no warranty for the work (except to the
+extent that warranties are provided), that licensees may convey the
+work under this License, and how to view a copy of this License.  If
+the interface presents a list of user commands or options, such as a
+menu, a prominent item in the list meets this criterion.
+
+  1. Source Code.
+
+  The "source code" for a work means the preferred form of the work
+for making modifications to it.  "Object code" means any non-source
+form of a work.
+
+  A "Standard Interface" means an interface that either is an official
+standard defined by a recognized standards body, or, in the case of
+interfaces specified for a particular programming language, one that
+is widely used among developers working in that language.
+
+  The "System Libraries" of an executable work include anything, other
+than the work as a whole, that (a) is included in the normal form of
+packaging a Major Component, but which is not part of that Major
+Component, and (b) serves only to enable use of the work with that
+Major Component, or to implement a Standard Interface for which an
+implementation is available to the public in source code form.  A
+"Major Component", in this context, means a major essential component
+(kernel, window system, and so on) of the specific operating system
+(if any) on which the executable work runs, or a compiler used to
+produce the work, or an object code interpreter used to run it.
+
+  The "Corresponding Source" for a work in object code form means all
+the source code needed to generate, install, and (for an executable
+work) run the object code and to modify the work, including scripts to
+control those activities.  However, it does not include the work's
+System Libraries, or general-purpose tools or generally available free
+programs which are used unmodified in performing those activities but
+which are not part of the work.  For example, Corresponding Source
+includes interface definition files associated with source files for
+the work, and the source code for shared libraries and dynamically
+linked subprograms that the work is specifically designed to require,
+such as by intimate data communication or control flow between those
+subprograms and other parts of the work.
+
+  The Corresponding Source need not include anything that users
+can regenerate automatically from other parts of the Corresponding
+Source.
+
+  The Corresponding Source for a work in source code form is that
+same work.
+
+  2. Basic Permissions.
+
+  All rights granted under this License are granted for the term of
+copyright on the Program, and are irrevocable provided the stated
+conditions are met.  This License explicitly affirms your unlimited
+permission to run the unmodified Program.  The output from running a
+covered work is covered by this License only if the output, given its
+content, constitutes a covered work.  This License acknowledges your
+rights of fair use or other equivalent, as provided by copyright law.
+
+  You may make, run and propagate covered works that you do not
+convey, without conditions so long as your license otherwise remains
+in force.  You may convey covered works to others for the sole purpose
+of having them make modifications exclusively for you, or provide you
+with facilities for running those works, provided that you comply with
+the terms of this License in conveying all material for which you do
+not control copyright.  Those thus making or running the covered works
+for you must do so exclusively on your behalf, under your direction
+and control, on terms that prohibit them from making any copies of
+your copyrighted material outside their relationship with you.
+
+  Conveying under any other circumstances is permitted solely under
+the conditions stated below.  Sublicensing is not allowed; section 10
+makes it unnecessary.
+
+  3. Protecting Users' Legal Rights From Anti-Circumvention Law.
+
+  No covered work shall be deemed part of an effective technological
+measure under any applicable law fulfilling obligations under article
+11 of the WIPO copyright treaty adopted on 20 December 1996, or
+similar laws prohibiting or restricting circumvention of such
+measures.
+
+  When you convey a covered work, you waive any legal power to forbid
+circumvention of technological measures to the extent such circumvention
+is effected by exercising rights under this License with respect to
+the covered work, and you disclaim any intention to limit operation or
+modification of the work as a means of enforcing, against the work's
+users, your or third parties' legal rights to forbid circumvention of
+technological measures.
+
+  4. Conveying Verbatim Copies.
+
+  You may convey verbatim copies of the Program's source code as you
+receive it, in any medium, provided that you conspicuously and
+appropriately publish on each copy an appropriate copyright notice;
+keep intact all notices stating that this License and any
+non-permissive terms added in accord with section 7 apply to the code;
+keep intact all notices of the absence of any warranty; and give all
+recipients a copy of this License along with the Program.
+
+  You may charge any price or no price for each copy that you convey,
+and you may offer support or warranty protection for a fee.
+
+  5. Conveying Modified Source Versions.
+
+  You may convey a work based on the Program, or the modifications to
+produce it from the Program, in the form of source code under the
+terms of section 4, provided that you also meet all of these conditions:
+
+    a) The work must carry prominent notices stating that you modified
+    it, and giving a relevant date.
+
+    b) The work must carry prominent notices stating that it is
+    released under this License and any conditions added under section
+    7.  This requirement modifies the requirement in section 4 to
+    "keep intact all notices".
+
+    c) You must license the entire work, as a whole, under this
+    License to anyone who comes into possession of a copy.  This
+    License will therefore apply, along with any applicable section 7
+    additional terms, to the whole of the work, and all its parts,
+    regardless of how they are packaged.  This License gives no
+    permission to license the work in any other way, but it does not
+    invalidate such permission if you have separately received it.
+
+    d) If the work has interactive user interfaces, each must display
+    Appropriate Legal Notices; however, if the Program has interactive
+    interfaces that do not display Appropriate Legal Notices, your
+    work need not make them do so.
+
+  A compilation of a covered work with other separate and independent
+works, which are not by their nature extensions of the covered work,
+and which are not combined with it such as to form a larger program,
+in or on a volume of a storage or distribution medium, is called an
+"aggregate" if the compilation and its resulting copyright are not
+used to limit the access or legal rights of the compilation's users
+beyond what the individual works permit.  Inclusion of a covered work
+in an aggregate does not cause this License to apply to the other
+parts of the aggregate.
+
+  6. Conveying Non-Source Forms.
+
+  You may convey a covered work in object code form under the terms
+of sections 4 and 5, provided that you also convey the
+machine-readable Corresponding Source under the terms of this License,
+in one of these ways:
+
+    a) Convey the object code in, or embodied in, a physical product
+    (including a physical distribution medium), accompanied by the
+    Corresponding Source fixed on a durable physical medium
+    customarily used for software interchange.
+
+    b) Convey the object code in, or embodied in, a physical product
+    (including a physical distribution medium), accompanied by a
+    written offer, valid for at least three years and valid for as
+    long as you offer spare parts or customer support for that product
+    model, to give anyone who possesses the object code either (1) a
+    copy of the Corresponding Source for all the software in the
+    product that is covered by this License, on a durable physical
+    medium customarily used for software interchange, for a price no
+    more than your reasonable cost of physically performing this
+    conveying of source, or (2) access to copy the
+    Corresponding Source from a network server at no charge.
+
+    c) Convey individual copies of the object code with a copy of the
+    written offer to provide the Corresponding Source.  This
+    alternative is allowed only occasionally and noncommercially, and
+    only if you received the object code with such an offer, in accord
+    with subsection 6b.
+
+    d) Convey the object code by offering access from a designated
+    place (gratis or for a charge), and offer equivalent access to the
+    Corresponding Source in the same way through the same place at no
+    further charge.  You need not require recipients to copy the
+    Corresponding Source along with the object code.  If the place to
+    copy the object code is a network server, the Corresponding Source
+    may be on a different server (operated by you or a third party)
+    that supports equivalent copying facilities, provided you maintain
+    clear directions next to the object code saying where to find the
+    Corresponding Source.  Regardless of what server hosts the
+    Corresponding Source, you remain obligated to ensure that it is
+    available for as long as needed to satisfy these requirements.
+
+    e) Convey the object code using peer-to-peer transmission, provided
+    you inform other peers where the object code and Corresponding
+    Source of the work are being offered to the general public at no
+    charge under subsection 6d.
+
+  A separable portion of the object code, whose source code is excluded
+from the Corresponding Source as a System Library, need not be
+included in conveying the object code work.
+
+  A "User Product" is either (1) a "consumer product", which means any
+tangible personal property which is normally used for personal, family,
+or household purposes, or (2) anything designed or sold for incorporation
+into a dwelling.  In determining whether a product is a consumer product,
+doubtful cases shall be resolved in favor of coverage.  For a particular
+product received by a particular user, "normally used" refers to a
+typical or common use of that class of product, regardless of the status
+of the particular user or of the way in which the particular user
+actually uses, or expects or is expected to use, the product.  A product
+is a consumer product regardless of whether the product has substantial
+commercial, industrial or non-consumer uses, unless such uses represent
+the only significant mode of use of the product.
+
+  "Installation Information" for a User Product means any methods,
+procedures, authorization keys, or other information required to install
+and execute modified versions of a covered work in that User Product from
+a modified version of its Corresponding Source.  The information must
+suffice to ensure that the continued functioning of the modified object
+code is in no case prevented or interfered with solely because
+modification has been made.
+
+  If you convey an object code work under this section in, or with, or
+specifically for use in, a User Product, and the conveying occurs as
+part of a transaction in which the right of possession and use of the
+User Product is transferred to the recipient in perpetuity or for a
+fixed term (regardless of how the transaction is characterized), the
+Corresponding Source conveyed under this section must be accompanied
+by the Installation Information.  But this requirement does not apply
+if neither you nor any third party retains the ability to install
+modified object code on the User Product (for example, the work has
+been installed in ROM).
+
+  The requirement to provide Installation Information does not include a
+requirement to continue to provide support service, warranty, or updates
+for a work that has been modified or installed by the recipient, or for
+the User Product in which it has been modified or installed.  Access to a
+network may be denied when the modification itself materially and
+adversely affects the operation of the network or violates the rules and
+protocols for communication across the network.
+
+  Corresponding Source conveyed, and Installation Information provided,
+in accord with this section must be in a format that is publicly
+documented (and with an implementation available to the public in
+source code form), and must require no special password or key for
+unpacking, reading or copying.
+
+  7. Additional Terms.
+
+  "Additional permissions" are terms that supplement the terms of this
+License by making exceptions from one or more of its conditions.
+Additional permissions that are applicable to the entire Program shall
+be treated as though they were included in this License, to the extent
+that they are valid under applicable law.  If additional permissions
+apply only to part of the Program, that part may be used separately
+under those permissions, but the entire Program remains governed by
+this License without regard to the additional permissions.
+
+  When you convey a copy of a covered work, you may at your option
+remove any additional permissions from that copy, or from any part of
+it.  (Additional permissions may be written to require their own
+removal in certain cases when you modify the work.)  You may place
+additional permissions on material, added by you to a covered work,
+for which you have or can give appropriate copyright permission.
+
+  Notwithstanding any other provision of this License, for material you
+add to a covered work, you may (if authorized by the copyright holders of
+that material) supplement the terms of this License with terms:
+
+    a) Disclaiming warranty or limiting liability differently from the
+    terms of sections 15 and 16 of this License; or
+
+    b) Requiring preservation of specified reasonable legal notices or
+    author attributions in that material or in the Appropriate Legal
+    Notices displayed by works containing it; or
+
+    c) Prohibiting misrepresentation of the origin of that material, or
+    requiring that modified versions of such material be marked in
+    reasonable ways as different from the original version; or
+
+    d) Limiting the use for publicity purposes of names of licensors or
+    authors of the material; or
+
+    e) Declining to grant rights under trademark law for use of some
+    trade names, trademarks, or service marks; or
+
+    f) Requiring indemnification of licensors and authors of that
+    material by anyone who conveys the material (or modified versions of
+    it) with contractual assumptions of liability to the recipient, for
+    any liability that these contractual assumptions directly impose on
+    those licensors and authors.
+
+  All other non-permissive additional terms are considered "further
+restrictions" within the meaning of section 10.  If the Program as you
+received it, or any part of it, contains a notice stating that it is
+governed by this License along with a term that is a further
+restriction, you may remove that term.  If a license document contains
+a further restriction but permits relicensing or conveying under this
+License, you may add to a covered work material governed by the terms
+of that license document, provided that the further restriction does
+not survive such relicensing or conveying.
+
+  If you add terms to a covered work in accord with this section, you
+must place, in the relevant source files, a statement of the
+additional terms that apply to those files, or a notice indicating
+where to find the applicable terms.
+
+  Additional terms, permissive or non-permissive, may be stated in the
+form of a separately written license, or stated as exceptions;
+the above requirements apply either way.
+
+  8. Termination.
+
+  You may not propagate or modify a covered work except as expressly
+provided under this License.  Any attempt otherwise to propagate or
+modify it is void, and will automatically terminate your rights under
+this License (including any patent licenses granted under the third
+paragraph of section 11).
+
+  However, if you cease all violation of this License, then your
+license from a particular copyright holder is reinstated (a)
+provisionally, unless and until the copyright holder explicitly and
+finally terminates your license, and (b) permanently, if the copyright
+holder fails to notify you of the violation by some reasonable means
+prior to 60 days after the cessation.
+
+  Moreover, your license from a particular copyright holder is
+reinstated permanently if the copyright holder notifies you of the
+violation by some reasonable means, this is the first time you have
+received notice of violation of this License (for any work) from that
+copyright holder, and you cure the violation prior to 30 days after
+your receipt of the notice.
+
+  Termination of your rights under this section does not terminate the
+licenses of parties who have received copies or rights from you under
+this License.  If your rights have been terminated and not permanently
+reinstated, you do not qualify to receive new licenses for the same
+material under section 10.
+
+  9. Acceptance Not Required for Having Copies.
+
+  You are not required to accept this License in order to receive or
+run a copy of the Program.  Ancillary propagation of a covered work
+occurring solely as a consequence of using peer-to-peer transmission
+to receive a copy likewise does not require acceptance.  However,
+nothing other than this License grants you permission to propagate or
+modify any covered work.  These actions infringe copyright if you do
+not accept this License.  Therefore, by modifying or propagating a
+covered work, you indicate your acceptance of this License to do so.
+
+  10. Automatic Licensing of Downstream Recipients.
+
+  Each time you convey a covered work, the recipient automatically
+receives a license from the original licensors, to run, modify and
+propagate that work, subject to this License.  You are not responsible
+for enforcing compliance by third parties with this License.
+
+  An "entity transaction" is a transaction transferring control of an
+organization, or substantially all assets of one, or subdividing an
+organization, or merging organizations.  If propagation of a covered
+work results from an entity transaction, each party to that
+transaction who receives a copy of the work also receives whatever
+licenses to the work the party's predecessor in interest had or could
+give under the previous paragraph, plus a right to possession of the
+Corresponding Source of the work from the predecessor in interest, if
+the predecessor has it or can get it with reasonable efforts.
+
+  You may not impose any further restrictions on the exercise of the
+rights granted or affirmed under this License.  For example, you may
+not impose a license fee, royalty, or other charge for exercise of
+rights granted under this License, and you may not initiate litigation
+(including a cross-claim or counterclaim in a lawsuit) alleging that
+any patent claim is infringed by making, using, selling, offering for
+sale, or importing the Program or any portion of it.
+
+  11. Patents.
+
+  A "contributor" is a copyright holder who authorizes use under this
+License of the Program or a work on which the Program is based.  The
+work thus licensed is called the contributor's "contributor version".
+
+  A contributor's "essential patent claims" are all patent claims
+owned or controlled by the contributor, whether already acquired or
+hereafter acquired, that would be infringed by some manner, permitted
+by this License, of making, using, or selling its contributor version,
+but do not include claims that would be infringed only as a
+consequence of further modification of the contributor version.  For
+purposes of this definition, "control" includes the right to grant
+patent sublicenses in a manner consistent with the requirements of
+this License.
+
+  Each contributor grants you a non-exclusive, worldwide, royalty-free
+patent license under the contributor's essential patent claims, to
+make, use, sell, offer for sale, import and otherwise run, modify and
+propagate the contents of its contributor version.
+
+  In the following three paragraphs, a "patent license" is any express
+agreement or commitment, however denominated, not to enforce a patent
+(such as an express permission to practice a patent or covenant not to
+sue for patent infringement).  To "grant" such a patent license to a
+party means to make such an agreement or commitment not to enforce a
+patent against the party.
+
+  If you convey a covered work, knowingly relying on a patent license,
+and the Corresponding Source of the work is not available for anyone
+to copy, free of charge and under the terms of this License, through a
+publicly available network server or other readily accessible means,
+then you must either (1) cause the Corresponding Source to be so
+available, or (2) arrange to deprive yourself of the benefit of the
+patent license for this particular work, or (3) arrange, in a manner
+consistent with the requirements of this License, to extend the patent
+license to downstream recipients.  "Knowingly relying" means you have
+actual knowledge that, but for the patent license, your conveying the
+covered work in a country, or your recipient's use of the covered work
+in a country, would infringe one or more identifiable patents in that
+country that you have reason to believe are valid.
+
+  If, pursuant to or in connection with a single transaction or
+arrangement, you convey, or propagate by procuring conveyance of, a
+covered work, and grant a patent license to some of the parties
+receiving the covered work authorizing them to use, propagate, modify
+or convey a specific copy of the covered work, then the patent license
+you grant is automatically extended to all recipients of the covered
+work and works based on it.
+
+  A patent license is "discriminatory" if it does not include within
+the scope of its coverage, prohibits the exercise of, or is
+conditioned on the non-exercise of one or more of the rights that are
+specifically granted under this License.  You may not convey a covered
+work if you are a party to an arrangement with a third party that is
+in the business of distributing software, under which you make payment
+to the third party based on the extent of your activity of conveying
+the work, and under which the third party grants, to any of the
+parties who would receive the covered work from you, a discriminatory
+patent license (a) in connection with copies of the covered work
+conveyed by you (or copies made from those copies), or (b) primarily
+for and in connection with specific products or compilations that
+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
+
+  Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+  12. No Surrender of Others' Freedom.
+
+  If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all.  For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+  13. Remote Network Interaction; Use with the GNU General Public License.
+
+  Notwithstanding any other provision of this License, if you modify the
+Program, your modified version must prominently offer all users
+interacting with it remotely through a computer network (if your version
+supports such interaction) an opportunity to receive the Corresponding
+Source of your version by providing access to the Corresponding Source
+from a network server at no charge, through some standard or customary
+means of facilitating copying of software.  This Corresponding Source
+shall include the Corresponding Source for any work covered by version 3
+of the GNU General Public License that is incorporated pursuant to the
+following paragraph.
+
+  Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU General Public License into a single
+combined work, and to convey the resulting work.  The terms of this
+License will continue to apply to the part which is the covered work,
+but the work with which it is combined will remain governed by version
+3 of the GNU General Public License.
+
+  14. Revised Versions of this License.
+
+  The Free Software Foundation may publish revised and/or new versions of
+the GNU Affero General Public License from time to time.  Such new versions
+will be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+  Each version is given a distinguishing version number.  If the
+Program specifies that a certain numbered version of the GNU Affero General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU Affero General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+  If the Program specifies that a proxy can decide which future
+versions of the GNU Affero General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If your software can interact with users remotely through a computer
+network, you should also make sure that it provides a way for users to
+get its source.  For example, if your program is a web application, its
+interface could display a "Source" link that leads users to an archive
+of the code.  There are many ways you could offer source, and different
+solutions will be better for different programs; see section 13 for the
+specific requirements.
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU AGPL, see
+<https://www.gnu.org/licenses/>.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000000000000000000000000000000000000..6f900cafbce74151cec50740a9ea175ce86bc189
--- /dev/null
+++ b/README.md
@@ -0,0 +1,9 @@
+# sinwon
+
+sinwon is a simple [OAuth 2] server for small deployments.
+
+## License
+
+AGPLv3 only, see LICENSE.
+
+[OAuth 2]: https://oauth.net/2/
diff --git a/db.go b/db.go
new file mode 100644
index 0000000000000000000000000000000000000000..c82dca8c118d5fd507ec9575f4b8413bc3e4f946
--- /dev/null
+++ b/db.go
@@ -0,0 +1,200 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	_ "embed"
+	"fmt"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+//go:embed schema.sql
+var schema string
+
+var errNoDBRows = sql.ErrNoRows
+
+type DB struct {
+	db *sql.DB
+}
+
+func openDB(filename string) (*DB, error) {
+	sqlDB, err := sql.Open("sqlite3", filename)
+	if err != nil {
+		return nil, err
+	}
+
+	db := &DB{sqlDB}
+	if err := db.init(context.TODO()); err != nil {
+		db.Close()
+		return nil, err
+	}
+
+	return db, nil
+}
+
+func (db *DB) init(ctx context.Context) error {
+	var n int
+	if err := db.db.QueryRowContext(ctx, "SELECT COUNT(*) FROM sqlite_schema").Scan(&n); err != nil {
+		return err
+	} else if n != 0 {
+		return nil
+	}
+
+	if _, err := db.db.ExecContext(ctx, schema); err != nil {
+		return err
+	}
+
+	// TODO: drop this
+	defaultUser := User{Username: "root"}
+	if err := defaultUser.SetPassword("root"); err != nil {
+		return err
+	}
+	return db.StoreUser(ctx, &defaultUser)
+}
+
+func (db *DB) Close() error {
+	return db.db.Close()
+}
+
+func (db *DB) FetchUser(ctx context.Context, username string) (*User, error) {
+	rows, err := db.db.QueryContext(ctx, "SELECT * FROM User WHERE username = ?", username)
+	if err != nil {
+		return nil, err
+	}
+	var user User
+	err = scanRow(&user, rows)
+	return &user, err
+}
+
+func (db *DB) StoreUser(ctx context.Context, user *User) error {
+	return db.db.QueryRowContext(ctx, `
+		INSERT INTO User(id, username, password_hash)
+		VALUES (:id, :username, :password_hash)
+		ON CONFLICT(id) DO UPDATE SET
+			username = :username,
+			password_hash = :password_hash
+		RETURNING id
+	`, entityArgs(user)...).Scan(&user.ID)
+}
+
+func (db *DB) FetchClient(ctx context.Context, clientID string) (*Client, error) {
+	rows, err := db.db.QueryContext(ctx, "SELECT * FROM Client WHERE client_id = ?", clientID)
+	if err != nil {
+		return nil, err
+	}
+	var client Client
+	err = scanRow(&client, rows)
+	return &client, err
+}
+
+func (db *DB) StoreClient(ctx context.Context, client *Client) error {
+	return db.db.QueryRowContext(ctx, `
+		INSERT INTO Client(id, client_id, client_secret_hash, owner)
+		VALUES (:id, :client_id, :client_secret_hash, :owner)
+		ON CONFLICT(id) DO UPDATE SET
+			client_id = :client_id,
+			client_secret_hash = :client_secret_hash,
+			owner = :owner
+		RETURNING id
+	`, entityArgs(client)...).Scan(&client.ID)
+}
+
+func (db *DB) ListClients(ctx context.Context, owner ID[*User]) ([]Client, error) {
+	rows, err := db.db.QueryContext(ctx, "SELECT * FROM Client WHERE owner IS ?", owner)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var l []Client
+	for rows.Next() {
+		var client Client
+		if err := scan(&client, rows); err != nil {
+			return nil, err
+		}
+		l = append(l, client)
+	}
+
+	return l, rows.Close()
+}
+
+func (db *DB) FetchAccessToken(ctx context.Context, id ID[*AccessToken]) (*AccessToken, error) {
+	rows, err := db.db.QueryContext(ctx, "SELECT * FROM AccessToken WHERE id = ?", id)
+	if err != nil {
+		return nil, err
+	}
+	var token AccessToken
+	err = scanRow(&token, rows)
+	return &token, err
+}
+
+func (db *DB) CreateAccessToken(ctx context.Context, token *AccessToken) error {
+	return db.db.QueryRowContext(ctx, `
+		INSERT INTO AccessToken(hash, user, client, scope, issued_at, expires_at)
+		VALUES (:hash, :user, :client, :scope, :issued_at, :expires_at)
+		RETURNING id
+	`, entityArgs(token)...).Scan(&token.ID)
+}
+
+func (db *DB) CreateAuthCode(ctx context.Context, code *AuthCode) error {
+	return db.db.QueryRowContext(ctx, `
+		INSERT INTO AuthCode(hash, created_at, user, client, scope)
+		VALUES (:hash, :created_at, :user, :client, :scope)
+		RETURNING id
+	`, entityArgs(code)...).Scan(&code.ID)
+}
+
+func (db *DB) PopAuthCode(ctx context.Context, id ID[*AuthCode]) (*AuthCode, error) {
+	rows, err := db.db.QueryContext(ctx, `
+		DELETE FROM AuthCode
+		WHERE id = ?
+		RETURNING *
+	`, id)
+	if err != nil {
+		return nil, err
+	}
+	var authCode AuthCode
+	err = scanRow(&authCode, rows)
+	return &authCode, err
+}
+
+func scan(e entity, rows *sql.Rows) error {
+	columns := e.columns()
+
+	keys, err := rows.Columns()
+	if err != nil {
+		panic(err)
+	}
+	out := make([]interface{}, len(keys))
+	for i, k := range keys {
+		v, ok := columns[k]
+		if !ok {
+			panic(fmt.Errorf("unknown column %q", k))
+		}
+		out[i] = v
+	}
+
+	return rows.Scan(out...)
+}
+
+func scanRow(e entity, rows *sql.Rows) error {
+	if !rows.Next() {
+		return sql.ErrNoRows
+	}
+	if err := scan(e, rows); err != nil {
+		return err
+	}
+	return rows.Close()
+}
+
+func entityArgs(e entity) []interface{} {
+	columns := e.columns()
+
+	l := make([]interface{}, 0, len(columns))
+	for k, v := range columns {
+		l = append(l, sql.Named(k, v))
+	}
+
+	return l
+}
diff --git a/entity.go b/entity.go
new file mode 100644
index 0000000000000000000000000000000000000000..a36750b99156715f6cd98b0b98c367b3531a92a3
--- /dev/null
+++ b/entity.go
@@ -0,0 +1,250 @@
+package main
+
+import (
+	"crypto/rand"
+	"crypto/sha512"
+	"crypto/subtle"
+	"database/sql"
+	"database/sql/driver"
+	"encoding/base64"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/crypto/bcrypt"
+)
+
+type entity interface {
+	columns() map[string]interface{}
+}
+
+var (
+	_ entity = (*User)(nil)
+	_ entity = (*Client)(nil)
+	_ entity = (*AccessToken)(nil)
+	_ entity = (*AuthCode)(nil)
+)
+
+type ID[T entity] int64
+
+var (
+	_ sql.Scanner   = (*ID[*User])(nil)
+	_ driver.Valuer = ID[*User](0)
+)
+
+func (ptr *ID[T]) Scan(v interface{}) error {
+	if v == nil {
+		*ptr = 0
+		return nil
+	}
+	id, ok := v.(int64)
+	if !ok {
+		return fmt.Errorf("cannot scan ID from %T", v)
+	}
+	*ptr = ID[T](id)
+	return nil
+}
+
+func (id ID[T]) Value() (driver.Value, error) {
+	if id == 0 {
+		return nil, nil
+	} else {
+		return int64(id), nil
+	}
+}
+
+type User struct {
+	ID           ID[*User]
+	Username     string
+	PasswordHash string
+}
+
+func (user *User) columns() map[string]interface{} {
+	return map[string]interface{}{
+		"id":            &user.ID,
+		"username":      &user.Username,
+		"password_hash": &user.PasswordHash,
+	}
+}
+
+func (user *User) VerifyPassword(password string) error {
+	// TODO: upgrade hash
+	return bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(password))
+}
+
+func (user *User) SetPassword(password string) error {
+	hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
+	if err != nil {
+		return err
+	}
+	user.PasswordHash = string(hash)
+	return nil
+}
+
+type Client struct {
+	ID               ID[*Client]
+	ClientID         string
+	ClientSecretHash []byte
+	Owner            ID[*User]
+}
+
+func NewClient(owner ID[*User]) (client *Client, secret string, err error) {
+	id, err := generateUID()
+	if err != nil {
+		return nil, "", fmt.Errorf("failed to generate client ID: %v", err)
+	}
+	secret, hash, err := generateSecret()
+	if err != nil {
+		return nil, "", fmt.Errorf("failed to generate client secret: %v", err)
+	}
+	client = &Client{
+		ClientID:         id,
+		ClientSecretHash: hash,
+		Owner:            owner,
+	}
+	return client, secret, nil
+}
+
+func (client *Client) columns() map[string]interface{} {
+	return map[string]interface{}{
+		"id":                 &client.ID,
+		"client_id":          &client.ClientID,
+		"client_secret_hash": &client.ClientSecretHash,
+		"owner":              &client.Owner,
+	}
+}
+
+func (client *Client) VerifySecret(secret string) bool {
+	return verifyHash(client.ClientSecretHash, secret)
+}
+
+type AccessToken struct {
+	ID        ID[*AccessToken]
+	Hash      []byte
+	User      ID[*User]
+	Client    ID[*Client]
+	Scope     string
+	IssuedAt  time.Time
+	ExpiresAt time.Time
+}
+
+func (token *AccessToken) Generate() (secret string, err error) {
+	secret, hash, err := generateSecret()
+	if err != nil {
+		return "", fmt.Errorf("failed to generate access token secret: %v", err)
+	}
+	token.Hash = hash
+	token.IssuedAt = time.Now()
+	token.ExpiresAt = time.Now().Add(2 * time.Hour)
+	return secret, nil
+}
+
+func NewAccessTokenFromAuthCode(authCode *AuthCode) (token *AccessToken, secret string, err error) {
+	token = &AccessToken{
+		User:   authCode.User,
+		Client: authCode.Client,
+		Scope:  authCode.Scope,
+	}
+	secret, err = token.Generate()
+	return token, secret, err
+}
+
+func (token *AccessToken) columns() map[string]interface{} {
+	return map[string]interface{}{
+		"id":         &token.ID,
+		"hash":       &token.Hash,
+		"user":       &token.User,
+		"client":     &token.Client,
+		"scope":      &token.Scope,
+		"issued_at":  &token.IssuedAt,
+		"expires_at": &token.ExpiresAt,
+	}
+}
+
+func (token *AccessToken) VerifySecret(secret string) bool {
+	return verifyHash(token.Hash, secret) && verifyExpiration(token.ExpiresAt)
+}
+
+type AuthCode struct {
+	ID        ID[*AuthCode]
+	Hash      []byte
+	CreatedAt time.Time
+	User      ID[*User]
+	Client    ID[*Client]
+	Scope     string
+}
+
+func NewAuthCode(user ID[*User], client ID[*Client], scope string) (code *AuthCode, secret string, err error) {
+	secret, hash, err := generateSecret()
+	if err != nil {
+		return nil, "", fmt.Errorf("failed to generate authentication code secret: %v", err)
+	}
+	code = &AuthCode{
+		Hash:      hash,
+		CreatedAt: time.Now(),
+		User:      user,
+		Client:    client,
+		Scope:     scope,
+	}
+	return code, secret, nil
+}
+
+func (code *AuthCode) columns() map[string]interface{} {
+	return map[string]interface{}{
+		"id":         &code.ID,
+		"hash":       &code.Hash,
+		"created_at": &code.CreatedAt,
+		"user":       &code.User,
+		"client":     &code.Client,
+		"scope":      &code.Scope,
+	}
+}
+
+func (code *AuthCode) VerifySecret(secret string) bool {
+	return verifyHash(code.Hash, secret) && verifyExpiration(code.CreatedAt.Add(10*time.Minute))
+}
+
+func UnmarshalSecret[T entity](s string) (id ID[T], secret string, err error) {
+	idStr, secret, _ := strings.Cut(s, ".")
+	u, _ := strconv.ParseUint(idStr, 10, 63)
+	if u == 0 {
+		return 0, "", fmt.Errorf("invalid ID")
+	}
+	return ID[T](int64(u)), secret, nil
+}
+
+func MarshalSecret[T entity](id ID[T], secret string) string {
+	if id == 0 {
+		panic("cannot marshal zero ID")
+	}
+	return fmt.Sprintf("%v.%v", int64(id), secret)
+}
+
+func generateUID() (string, error) {
+	b := make([]byte, 32)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	return base64.RawURLEncoding.EncodeToString(b), nil
+}
+
+func generateSecret() (secret string, hash []byte, err error) {
+	b := make([]byte, 32)
+	if _, err := rand.Read(b); err != nil {
+		return "", nil, err
+	}
+	secret = base64.RawURLEncoding.EncodeToString(b)
+	h := sha512.Sum512(b)
+	return secret, h[:], nil
+}
+
+func verifyHash(hash []byte, secret string) bool {
+	b, _ := base64.RawURLEncoding.DecodeString(secret)
+	h := sha512.Sum512(b)
+	return subtle.ConstantTimeCompare(hash, h[:]) == 1
+}
+
+func verifyExpiration(t time.Time) bool {
+	return time.Now().Before(t)
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000000000000000000000000000000000000..f018bc3bff05bbae305654ca776db0f94fa88ada
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,9 @@
+module git.sr.ht/~emersion/sinwon
+
+go 1.18
+
+require git.sr.ht/~emersion/go-oauth2 v0.0.0-20240217160856-2e0d6e20b088
+
+require github.com/mattn/go-sqlite3 v1.14.22
+
+require golang.org/x/crypto v0.19.0
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000000000000000000000000000000000000..60037c555ec59aedaa4213ee86cc41a321570537
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,6 @@
+git.sr.ht/~emersion/go-oauth2 v0.0.0-20240217160856-2e0d6e20b088 h1:KuPliLD8CQM1WbCHdjHR6mhadIzLaAJCNENmvB1y9gs=
+git.sr.ht/~emersion/go-oauth2 v0.0.0-20240217160856-2e0d6e20b088/go.mod h1:VHj0jSCLIkrfEwmOvJ4+ykpoVbD/YLN7BM523oKKBHc=
+github.com/mattn/go-sqlite3 v1.14.22 h1:2gZY6PC6kBnID23Tichd1K+Z0oS6nE/XwU+Vz/5o4kU=
+github.com/mattn/go-sqlite3 v1.14.22/go.mod h1:Uh1q+B4BYcTPb+yiD3kU8Ct7aC0hY9fxUwlHK0RXw+Y=
+golang.org/x/crypto v0.19.0 h1:ENy+Az/9Y1vSrlrvBSyna3PITt4tiZLf7sgCjZBX7Wo=
+golang.org/x/crypto v0.19.0/go.mod h1:Iy9bg/ha4yyC70EfRS8jz+B6ybOBKMaSxLj6P6oBDfU=
diff --git a/main.go b/main.go
new file mode 100644
index 0000000000000000000000000000000000000000..e42c8098beaf5146b92e35a7127e9811eeb0fdb8
--- /dev/null
+++ b/main.go
@@ -0,0 +1,451 @@
+package main
+
+import (
+	"context"
+	"embed"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"html/template"
+	"io"
+	"log"
+	"mime"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"git.sr.ht/~emersion/go-oauth2"
+)
+
+var (
+	//go:embed template
+	templateFS embed.FS
+	//go:embed static
+	staticFS embed.FS
+)
+
+func main() {
+	var listenAddr string
+	flag.StringVar(&listenAddr, "listen", ":8080", "HTTP listen address")
+	flag.Parse()
+
+	tpl := template.Must(template.ParseFS(templateFS, "template/*.html"))
+
+	db, err := openDB("sinwon.db")
+	if err != nil {
+		log.Fatalf("Failed to open DB: %v", err)
+	}
+
+	mux := http.NewServeMux()
+	mux.Handle("/static/*", http.FileServer(http.FS(staticFS)))
+
+	mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
+		ctx := req.Context()
+
+		loginToken := loginTokenFromContext(ctx)
+		if loginToken == nil {
+			http.Redirect(w, req, "/login", http.StatusFound)
+			return
+		}
+
+		clients, err := db.ListClients(ctx, loginToken.User)
+		if err != nil {
+			httpError(w, err)
+			return
+		}
+
+		if err := tpl.ExecuteTemplate(w, "index.html", clients); err != nil {
+			panic(err)
+		}
+	})
+
+	mux.HandleFunc("/client/new", func(w http.ResponseWriter, req *http.Request) {
+		ctx := req.Context()
+
+		loginToken := loginTokenFromContext(ctx)
+		if loginToken == nil {
+			http.Redirect(w, req, "/login", http.StatusFound)
+			return
+		}
+
+		client, clientSecret, err := NewClient(loginToken.User)
+		if err != nil {
+			httpError(w, err)
+			return
+		}
+		if err := db.StoreClient(ctx, client); err != nil {
+			httpError(w, err)
+			return
+		}
+
+		data := struct {
+			ClientID     string
+			ClientSecret string
+		}{
+			ClientID:     client.ClientID,
+			ClientSecret: clientSecret,
+		}
+		if err := tpl.ExecuteTemplate(w, "client-secret.html", &data); err != nil {
+			panic(err)
+		}
+	})
+
+	mux.HandleFunc("/login", func(w http.ResponseWriter, req *http.Request) {
+		ctx := req.Context()
+
+		q := req.URL.Query()
+		rawRedirectURI := q.Get("redirect_uri")
+		if rawRedirectURI == "" {
+			rawRedirectURI = "/"
+		}
+
+		redirectURI, err := url.Parse(rawRedirectURI)
+		if err != nil || redirectURI.Scheme != "" || redirectURI.Opaque != "" || redirectURI.User != nil || redirectURI.Host != "" {
+			http.Error(w, "Invalid redirect URI", http.StatusBadRequest)
+			return
+		}
+
+		if loginTokenFromContext(ctx) != nil {
+			http.Redirect(w, req, redirectURI.String(), http.StatusFound)
+			return
+		}
+
+		username := req.PostFormValue("username")
+		password := req.PostFormValue("password")
+		if username == "" {
+			if err := tpl.ExecuteTemplate(w, "login.html", nil); err != nil {
+				panic(err)
+			}
+			return
+		}
+
+		user, err := db.FetchUser(ctx, username)
+		if err != nil && err != errNoDBRows {
+			httpError(w, fmt.Errorf("failed to fetch user: %v", err))
+			return
+		}
+		if err == nil {
+			err = user.VerifyPassword(password)
+		}
+		if err != nil {
+			log.Printf("login failed for user %q: %v", username, err)
+			// TODO: show error message
+			if err := tpl.ExecuteTemplate(w, "login.html", nil); err != nil {
+				panic(err)
+			}
+			return
+		}
+
+		token := AccessToken{
+			User:  user.ID,
+			Scope: internalTokenScope,
+		}
+		secret, err := token.Generate()
+		if err != nil {
+			httpError(w, fmt.Errorf("failed to generate access token: %v", err))
+			return
+		}
+		if err := db.CreateAccessToken(ctx, &token); err != nil {
+			httpError(w, fmt.Errorf("failed to create access token: %v", err))
+			return
+		}
+
+		setLoginTokenCookie(w, &token, secret)
+		http.Redirect(w, req, redirectURI.String(), http.StatusFound)
+	})
+
+	mux.HandleFunc("/authorize", func(w http.ResponseWriter, req *http.Request) {
+		ctx := req.Context()
+
+		q := req.URL.Query()
+		respType := oauth2.ResponseType(q.Get("response_type"))
+		clientID := q.Get("client_id")
+		rawRedirectURI := q.Get("redirect_uri")
+		scope := q.Get("scope")
+		state := q.Get("state")
+
+		if clientID == "" {
+			http.Error(w, "Missing client ID", http.StatusBadRequest)
+			return
+		}
+
+		client, err := db.FetchClient(ctx, clientID)
+		if err == errNoDBRows {
+			http.Error(w, "Invalid client ID", http.StatusForbidden)
+			return
+		} else if err != nil {
+			httpError(w, fmt.Errorf("failed to fetch client: %v", err))
+			return
+		}
+
+		// TODO: validate redirect URI with client
+		// TODO: make redirect URI optional
+		redirectURI, err := url.Parse(rawRedirectURI)
+		if err != nil {
+			http.Error(w, "Invalid redirect URI", http.StatusBadRequest)
+			return
+		}
+
+		if respType != oauth2.ResponseTypeCode {
+			redirectClientError(w, req, redirectURI, state, &oauth2.Error{
+				Code: oauth2.ErrorCodeUnsupportedResponseType,
+			})
+			return
+		}
+
+		// TODO: add support for scope
+		if scope != "" {
+			redirectClientError(w, req, redirectURI, state, &oauth2.Error{
+				Code: oauth2.ErrorCodeInvalidScope,
+			})
+			return
+		}
+
+		loginToken := loginTokenFromContext(ctx)
+		if loginToken == nil {
+			q := make(url.Values)
+			q.Set("redirect_uri", req.URL.String())
+			u := url.URL{
+				Path:     "/login",
+				RawQuery: q.Encode(),
+			}
+			http.Redirect(w, req, u.String(), http.StatusFound)
+			return
+		}
+
+		_ = req.ParseForm()
+		if _, ok := req.PostForm["authorize"]; !ok {
+			if err := tpl.ExecuteTemplate(w, "authorize.html", nil); err != nil {
+				panic(err)
+			}
+			return
+		}
+
+		authCode, secret, err := NewAuthCode(loginToken.User, client.ID, scope)
+		if err != nil {
+			httpError(w, fmt.Errorf("failed to generate authentication code: %v", err))
+			return
+		}
+
+		if err := db.CreateAuthCode(ctx, authCode); err != nil {
+			httpError(w, fmt.Errorf("failed to create authentication code: %v", err))
+			return
+		}
+
+		code := MarshalSecret(authCode.ID, secret)
+
+		values := make(url.Values)
+		values.Set("code", code)
+		if state != "" {
+			values.Set("state", state)
+		}
+		redirectClient(w, req, redirectURI, values)
+	})
+
+	mux.HandleFunc("/token", func(w http.ResponseWriter, req *http.Request) {
+		ctx := req.Context()
+
+		values, err := parseRequestBody(req)
+		if err != nil {
+			oauthError(w, &oauth2.Error{
+				Code:        oauth2.ErrorCodeInvalidRequest,
+				Description: err.Error(),
+			})
+			return
+		}
+
+		clientID := values.Get("client_id")
+		grantType := oauth2.GrantType(values.Get("grant_type"))
+		scope := values.Get("scope")
+
+		authClientID, clientSecret, _ := req.BasicAuth()
+		if clientID == "" && authClientID == "" {
+			oauthError(w, &oauth2.Error{
+				Code:        oauth2.ErrorCodeInvalidRequest,
+				Description: "Missing client ID",
+			})
+			return
+		} else if clientID == "" {
+			clientID = authClientID
+		} else if clientID != authClientID {
+			oauthError(w, &oauth2.Error{
+				Code:        oauth2.ErrorCodeInvalidRequest,
+				Description: "Client ID in request body doesn't match Authorization header field",
+			})
+			return
+		}
+
+		client, err := db.FetchClient(ctx, clientID)
+		if err == errNoDBRows {
+			oauthError(w, &oauth2.Error{
+				Code:        oauth2.ErrorCodeInvalidClient,
+				Description: "Invalid client ID",
+			})
+			return
+		} else if err != nil {
+			oauthError(w, fmt.Errorf("failed to fetch client: %v", err))
+			return
+		}
+
+		if client.ClientSecretHash != nil {
+			if !client.VerifySecret(clientSecret) {
+				oauthError(w, &oauth2.Error{
+					Code:        oauth2.ErrorCodeAccessDenied,
+					Description: "Invalid client secret",
+				})
+				return
+			}
+		}
+
+		if grantType != oauth2.GrantTypeAuthorizationCode {
+			oauthError(w, &oauth2.Error{
+				Code:        oauth2.ErrorCodeUnsupportedGrantType,
+				Description: "Unsupported grant type",
+			})
+			return
+		}
+
+		codeID, codeSecret, _ := UnmarshalSecret[*AuthCode](values.Get("code"))
+		authCode, err := db.PopAuthCode(ctx, codeID)
+		if err == errNoDBRows || (err == nil && !authCode.VerifySecret(codeSecret)) || authCode.Client != client.ID {
+			oauthError(w, &oauth2.Error{
+				Code:        oauth2.ErrorCodeAccessDenied,
+				Description: "Invalid authorization code",
+			})
+			return
+		} else if err != nil {
+			oauthError(w, fmt.Errorf("failed to fetch authorization code: %v", err))
+			return
+		}
+
+		if scope != authCode.Scope {
+			oauthError(w, &oauth2.Error{
+				Code:        oauth2.ErrorCodeAccessDenied,
+				Description: "Invalid scope",
+			})
+			return
+		}
+
+		// TODO: check redirect_uri
+
+		token, secret, err := NewAccessTokenFromAuthCode(authCode)
+		if err != nil {
+			oauthError(w, err)
+			return
+		}
+
+		if err := db.CreateAccessToken(ctx, token); err != nil {
+			oauthError(w, fmt.Errorf("failed to create access token: %v", err))
+			return
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Cache-Control", "no-store")
+		json.NewEncoder(w).Encode(&oauth2.TokenResp{
+			AccessToken: secret,
+			TokenType:   oauth2.TokenTypeBearer,
+			ExpiresIn:   time.Until(token.ExpiresAt),
+			Scope:       strings.Split(token.Scope, " "),
+		})
+	})
+
+	server := http.Server{
+		Addr:    listenAddr,
+		Handler: loginTokenMiddleware(mux),
+		BaseContext: func(net.Listener) context.Context {
+			return newBaseContext(db)
+		},
+	}
+	log.Printf("OAuth server listening on %v", server.Addr)
+	if err := server.ListenAndServe(); err != nil {
+		log.Fatalf("Failed to listen and serve: %v", err)
+	}
+}
+
+func parseRequestBody(req *http.Request) (url.Values, error) {
+	ct := req.Header.Get("Content-Type")
+	if ct != "" {
+		mimeType, _, err := mime.ParseMediaType(req.Header.Get("Content-Type"))
+		if err != nil {
+			return nil, fmt.Errorf("malformed Content-Type header field")
+		} else if mimeType != "application/x-www-form-urlencoded" {
+			return nil, fmt.Errorf("unsupported request content type")
+		}
+	}
+
+	r := io.LimitReader(req.Body, 10<<20)
+	b, err := io.ReadAll(r)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read request body: %v", err)
+	}
+
+	values, err := url.ParseQuery(string(b))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse request body: %v", err)
+	}
+
+	return values, nil
+}
+
+func httpError(w http.ResponseWriter, err error) {
+	log.Print(err)
+	http.Error(w, "Internal server error", http.StatusInternalServerError)
+}
+
+func oauthError(w http.ResponseWriter, err error) {
+	var oauthErr *oauth2.Error
+	if !errors.As(err, &oauthErr) {
+		oauthErr = &oauth2.Error{Code: oauth2.ErrorCodeServerError}
+		log.Print(err)
+	}
+
+	statusCode := http.StatusInternalServerError
+	switch oauthErr.Code {
+	case oauth2.ErrorCodeInvalidRequest, oauth2.ErrorCodeUnsupportedResponseType, oauth2.ErrorCodeInvalidScope, oauth2.ErrorCodeInvalidClient, oauth2.ErrorCodeInvalidGrant, oauth2.ErrorCodeUnsupportedGrantType:
+		statusCode = http.StatusBadRequest
+	case oauth2.ErrorCodeUnauthorizedClient, oauth2.ErrorCodeAccessDenied:
+		statusCode = http.StatusForbidden
+	case oauth2.ErrorCodeTemporarilyUnavailable:
+		statusCode = http.StatusServiceUnavailable
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(statusCode)
+	json.NewEncoder(w).Encode(oauthErr)
+}
+
+func redirectClient(w http.ResponseWriter, req *http.Request, redirectURI *url.URL, values url.Values) {
+	q := redirectURI.Query()
+	for k, v := range values {
+		q[k] = v
+	}
+
+	u := *redirectURI
+	u.RawQuery = q.Encode()
+
+	http.Redirect(w, req, u.String(), http.StatusFound)
+}
+
+func redirectClientError(w http.ResponseWriter, req *http.Request, redirectURI *url.URL, state string, err error) {
+	var oauthErr *oauth2.Error
+	if !errors.As(err, &oauthErr) {
+		oauthErr = &oauth2.Error{Code: oauth2.ErrorCodeServerError}
+		log.Print(err)
+	}
+
+	values := make(url.Values)
+	values.Set("error", string(oauthErr.Code))
+	if oauthErr.Description != "" {
+		values.Set("error_description", oauthErr.Description)
+	}
+	if oauthErr.URI != "" {
+		values.Set("error_uri", oauthErr.URI)
+	}
+	if state != "" {
+		values.Set("state", state)
+	}
+	redirectClient(w, req, redirectURI, values)
+}
diff --git a/middleware.go b/middleware.go
new file mode 100644
index 0000000000000000000000000000000000000000..d49cd0a87590414171e471ee1b4fc9c2ebcb61f5
--- /dev/null
+++ b/middleware.go
@@ -0,0 +1,82 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+)
+
+const internalTokenScope = "_sinwon"
+
+type contextKey string
+
+const (
+	contextKeyDB         = "db"
+	contextKeyLoginToken = "login-token"
+)
+
+func dbFromContext(ctx context.Context) *DB {
+	return ctx.Value(contextKeyDB).(*DB)
+}
+
+func loginTokenFromContext(ctx context.Context) *AccessToken {
+	v := ctx.Value(contextKeyLoginToken)
+	if v == nil {
+		return nil
+	}
+	return v.(*AccessToken)
+}
+
+func newBaseContext(db *DB) context.Context {
+	return context.WithValue(context.Background(), contextKeyDB, db)
+}
+
+func setLoginTokenCookie(w http.ResponseWriter, token *AccessToken, secret string) {
+	http.SetCookie(w, &http.Cookie{
+		Name:     "sinwon-token",
+		Value:    MarshalSecret(token.ID, secret),
+		HttpOnly: true,
+		SameSite: http.SameSiteStrictMode,
+		// TODO: Secure
+	})
+}
+
+func loginTokenMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		cookie, _ := req.Cookie("sinwon-token")
+		if cookie == nil {
+			next.ServeHTTP(w, req)
+			return
+		}
+
+		ctx := req.Context()
+		db := dbFromContext(ctx)
+		tokenID, tokenSecret, _ := UnmarshalSecret[*AccessToken](cookie.Value)
+		token, err := db.FetchAccessToken(ctx, tokenID)
+		if err == errNoDBRows || (err == nil && !token.VerifySecret(tokenSecret)) {
+			http.SetCookie(w, &http.Cookie{
+				Name:     "sinwon-token",
+				HttpOnly: true,
+				SameSite: http.SameSiteStrictMode,
+				MaxAge:   -1,
+			})
+			next.ServeHTTP(w, req)
+			return
+		} else if err != nil {
+			httpError(w, fmt.Errorf("failed to fetch access token: %v", err))
+			return
+		}
+
+		if token.Scope != internalTokenScope {
+			http.Error(w, "Invalid login token scope", http.StatusForbidden)
+			return
+		}
+		if token.User == 0 {
+			panic("login token with zero user ID")
+		}
+
+		ctx = context.WithValue(ctx, contextKeyLoginToken, token)
+		req = req.WithContext(ctx)
+		next.ServeHTTP(w, req)
+	})
+}
diff --git a/schema.sql b/schema.sql
new file mode 100644
index 0000000000000000000000000000000000000000..1a0a7e78ee5cb1998e506605de3c9ccd5dcb298e
--- /dev/null
+++ b/schema.sql
@@ -0,0 +1,38 @@
+PRAGMA user_version = 1;
+
+CREATE TABLE User (
+	id INTEGER PRIMARY KEY,
+	username TEXT NOT NULL UNIQUE,
+	password_hash TEXT
+);
+
+CREATE TABLE Client (
+	id INTEGER PRIMARY KEY,
+	client_id TEXT NOT NULL UNIQUE,
+	client_secret_hash BLOB,
+	owner INTEGER,
+	FOREIGN KEY(owner) REFERENCES User(id)
+);
+
+CREATE TABLE AccessToken (
+	id INTEGER PRIMARY KEY,
+	hash BLOB NOT NULL UNIQUE,
+	user INTEGER NOT NULL,
+	client INTEGER,
+	scope TEXT,
+	issued_at datetime NOT NULL,
+	expires_at datetime NOT NULL,
+	FOREIGN KEY(user) REFERENCES User(id),
+	FOREIGN KEY(client) REFERENCES Client(id)
+);
+
+CREATE TABLE AuthCode (
+	id INTEGER PRIMARY KEY,
+	hash BLOB NOT NULL UNIQUE,
+	created_at datetime NOT NULL,
+	user INTEGER NOT NULL,
+	client INTEGER NOT NULL,
+	scope TEXT,
+	FOREIGN KEY(user) REFERENCES User(id),
+	FOREIGN KEY(client) REFERENCES Client(id)
+);
diff --git a/static/style.css b/static/style.css
new file mode 100644
index 0000000000000000000000000000000000000000..f846fe8ea1fc793053c08ef26fafa5a2b13c3584
--- /dev/null
+++ b/static/style.css
@@ -0,0 +1,9 @@
+body {
+	font-family: sans-serif;
+	margin: 0;
+}
+main {
+	padding: 0 5px;
+	max-width: 800px;
+	margin: 0 auto;
+}
diff --git a/template/authorize.html b/template/authorize.html
new file mode 100644
index 0000000000000000000000000000000000000000..48d9f282b17696adbb311d1f730a036d2e9065a9
--- /dev/null
+++ b/template/authorize.html
@@ -0,0 +1,15 @@
+{{ template "head.html" }}
+
+<main>
+
+<h1>sinwon</h1>
+
+<p>Authorize client?</p>
+
+<form method="post" action="">
+	<button type="submit" name="authorize">Authorize</button>
+</form>
+
+</main>
+
+{{ template "foot.html" }}
diff --git a/template/client-secret.html b/template/client-secret.html
new file mode 100644
index 0000000000000000000000000000000000000000..d354b0e24aace063af3c9c6d8c43b4529dd056c2
--- /dev/null
+++ b/template/client-secret.html
@@ -0,0 +1,16 @@
+{{ template "head.html" }}
+
+<main>
+
+<h1>sinwon</h1>
+
+<p>
+	<strong>Client ID</strong>: <code>{{ .ClientID }}</code><br>
+	<strong>Client secret</strong>: <code>{{.ClientSecret}}</code>
+</p>
+
+<a href="/">Back</a>
+
+</main>
+
+{{ template "foot.html" }}
diff --git a/template/foot.html b/template/foot.html
new file mode 100644
index 0000000000000000000000000000000000000000..308b1d01b6ca1e7ab1b1fa896e6a8497bbcd1a37
--- /dev/null
+++ b/template/foot.html
@@ -0,0 +1,2 @@
+</body>
+</html>
diff --git a/template/head.html b/template/head.html
new file mode 100644
index 0000000000000000000000000000000000000000..4e67adfceb075951639c24ee864f07857f08bcbe
--- /dev/null
+++ b/template/head.html
@@ -0,0 +1,9 @@
+<!DOCTYPE HTML>
+<html lang="en">
+<head>
+    <meta charset="utf-8"/>
+    <title>sinwon</title>
+    <meta name="viewport" content="width=device-width, initial-scale=1"/>
+    <link rel="stylesheet" href="/static/style.css"/>
+</head>
+<body>
diff --git a/template/index.html b/template/index.html
new file mode 100644
index 0000000000000000000000000000000000000000..06c442c3dd5a9b4e13cdc6fd7809b0738bdf6abd
--- /dev/null
+++ b/template/index.html
@@ -0,0 +1,24 @@
+{{ template "head.html" }}
+
+<main>
+
+<h1>sinwon</h1>
+
+<form method="post" action="/client/new">
+	<button type="submit">Register new client</button>
+</form>
+
+{{ with . }}
+	<p>{{ . | len }} clients registered:</p>
+	<ul>
+		{{ range . }}
+			<li><code>{{ .ClientID }}</code></li>
+		{{ end }}
+	</ul>
+{{ else }}
+	<p>No client registered yet.</p>
+{{ end }}
+
+</main>
+
+{{ template "foot.html" }}
diff --git a/template/login.html b/template/login.html
new file mode 100644
index 0000000000000000000000000000000000000000..9f93f2a41a411a6a8a237c84906d2084360177b0
--- /dev/null
+++ b/template/login.html
@@ -0,0 +1,15 @@
+{{ template "head.html" }}
+
+<main>
+
+<h1>sinwon</h1>
+
+<form method="post" action="">
+	Username: <input type="text" name="username" autocomplete="username"><br>
+	Password: <input type="password" name="password"><br>
+	<button type="submit">Login</button>
+</form>
+
+</main>
+
+{{ template "foot.html" }}

-- 
2.48.1