Add single sign-on support via SSPI on Windows (#8463)

* Add single sign-on support via SSPI on Windows

* Ensure plugins implement interface

* Ensure plugins implement interface

* Move functions used only by the SSPI auth method to sspi_windows.go

* Field SSPISeparatorReplacement of AuthenticationForm should not be required via binding, as binding will insist the field is non-empty even if another login type is selected

* Fix breaking of oauth authentication on download links. Do not create new session with SSPI authentication on download links.

* Update documentation for the new 'SPNEGO with SSPI' login source

* Mention in documentation that ROOT_URL should contain the FQDN of the server

* Make sure that Contexter is not checking for active login sources when the ORM engine is not initialized (eg. when installing)

* Always initialize and free SSO methods, even if they are not enabled, as a method can be activated while the app is running (from Authentication sources)

* Add option in SSPIConfig for removing of domains from logon names

* Update helper text for StripDomainNames option

* Make sure handleSignIn() is called after a new user object is created by SSPI auth method

* Remove default value from text of form field helper

Co-Authored-By: Lauris BH <lauris@nix.lv>

* Remove default value from text of form field helper

Co-Authored-By: Lauris BH <lauris@nix.lv>

* Remove default value from text of form field helper

Co-Authored-By: Lauris BH <lauris@nix.lv>

* Only make a query to the DB to check if SSPI is enabled on handlers that need that information for templates

* Remove code duplication

* Log errors in ActiveLoginSources

Co-Authored-By: Lauris BH <lauris@nix.lv>

* Revert suffix of randomly generated E-mails for Reverse proxy authentication

Co-Authored-By: Lauris BH <lauris@nix.lv>

* Revert unneeded white-space change in template

Co-Authored-By: Lauris BH <lauris@nix.lv>

* Add copyright comments at the top of new files

* Use loopback name for randomly generated emails

* Add locale tag for the SSPISeparatorReplacement field with proper casing

* Revert casing of SSPISeparatorReplacement field in locale file, moving it up, next to other form fields

* Update docs/content/doc/features/authentication.en-us.md

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* Remove Priority() method and define the order in which SSO auth methods should be executed in one place

* Log authenticated username only if it's not empty

* Rephrase helper text for automatic creation of users

* Return error if more than one active SSPI auth source is found

* Change newUser() function to return error, letting caller log/handle the error

* Move isPublicResource, isPublicPage and handleSignIn functions outside SSPI auth method to allow other SSO methods to reuse them if needed

* Refactor initialization of the list containing SSO auth methods

* Validate SSPI settings on POST

* Change SSPI to only perform authentication on its own login page, API paths and download links. Leave Toggle middleware to redirect non authenticated users to login page

* Make 'Default language' in SSPI config empty, unless changed by admin

* Show error if admin tries to add a second authentication source of type SSPI

* Simplify declaration of global variable

* Rebuild gitgraph.js on Linux

* Make sure config values containing only whitespace are not accepted

1 files changed, 39 insertions, 0 deletions

diff --git a/docs/content/doc/features/authentication.en-us.md b/docs/content/doc/features/authentication.en-us.md
index afa9219676..be2e32db63 100644
--- a/docs/content/doc/features/authentication.en-us.md
+++ b/docs/content/doc/features/authentication.en-us.md
@@ -216,3 +216,42 @@ configure this, set the fields below:
 
 - Log in to Gitea as an Administrator and click on "Authentication" under Admin Panel.
   Then click `Add New Source` and fill in the details, changing all where appropriate.
+
+## SPNEGO with SSPI (Kerberos/NTLM, for Windows only)
+
+Gitea supports SPNEGO single sign-on authentication (the scheme defined by RFC4559) for the web part of the server via the Security Support Provider Interface (SSPI) built in Windows. SSPI works only in Windows environments - when both the server and the clients are running Windows.
+
+Before activating SSPI single sign-on authentication (SSO) you have to prepare your environment:
+
+- Create a separate user account in active directory, under which the `gitea.exe` process will be running (eg. `user` under domain `domain.local`):
+
+- Create a service principal name for the host where `gitea.exe` is running with class `HTTP`:
+  - Start `Command Prompt` or `PowerShell` as a priviledged domain user (eg. Domain Administrator)
+  - Run the command below, replacing `host.domain.local` with the fully qualified domain name (FQDN) of the server where the web application will be running, and `domain\user` with the name of the account created in the previous step:
+  ```
+    setspn -A HTTP/host.domain.local domain\user
+  ```
+
+- Sign in (*sign out if you were already signed in*) with the user created
+
+- Make sure that `ROOT_URL` in the `[server]` section of `custom/conf/app.ini` is the fully qualified domain name of the server where the web application will be running - the same you used when creating the service principal name (eg. `host.domain.local`)
+
+- Start the web server (`gitea.exe web`)
+
+- Enable SSPI authentication by adding an `SPNEGO with SSPI` authentication source in `Site Administration -> Authentication Sources`
+
+- Sign in to a client computer in the same domain with any domain user (client computer, different from the server running `gitea.exe`)
+
+- If you are using Chrome, Edge or Internet Explorer, add the URL of the web app to the Local intranet sites (`Internet Options -> Security -> Local intranet -> Sites`)
+
+- Start Chrome, Edge or Internet Explorer and navigate to the FQDN URL of gitea (eg. `http://host.domain.local:3000`)
+
+- Click the `Sign In` button on the dashboard and choose SSPI to be automatically logged in with the same user that is currently logged on to the computer
+
+- If it does not work, make sure that:
+  - You are not running the web browser on the same server where gitea is running. You should be running the web browser on a domain joined computer (client) that is different from the server. If both the client and server are runnning on the same computer NTLM will be prefered over Kerberos.
+  - There is only one `HTTP/...` SPN for the host
+  - The SPN contains only the hostname, without the port
+  - You have added the URL of the web app to the `Local intranet zone`
+  - The clocks of the server and client should not differ with more than 5 minutes (depends on group policy)
+  - `Integrated Windows Authentication` should be enabled in Internet Explorer (under `Advanced settings`)