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

options/locale/locale_en-US.ini

@@ -270,6 +270,7 @@ authorize_title = Authorize "%s" to access your account?
 authorization_failed = Authorization failed
 authorization_failed_desc = The authorization failed because we detected an invalid request. Please contact the maintainer of the app you've tried to authorize.
 disable_forgot_password_mail = Account recovery is disabled. Please contact your site administrator.
+sspi_auth_failed = SSPI authentication failed
 
 [mail]
 activate_account = Please activate your account
@@ -303,6 +304,9 @@ CommitChoice = Commit choice
 TreeName = File path
 Content = Content
 
+SSPISeparatorReplacement = Separator
+SSPIDefaultLanguage = Default Language
+
 require_error = ` cannot be empty.`
 alpha_dash_error = ` should contain only alphanumeric, dash ('-') and underscore ('_') characters.`
 alpha_dash_dot_error = ` should contain only alphanumeric, dash ('-'), underscore ('_') and dot ('.') characters.`
@@ -317,6 +321,7 @@ glob_pattern_error = ` glob pattern is invalid: %s.`
 unknown_error = Unknown error:
 captcha_incorrect = The CAPTCHA code is incorrect.
 password_not_match = The passwords do not match.
+lang_select_error = Select a language from the list.
 
 username_been_taken = The username is already taken.
 repo_name_been_taken = The repository name is already used.
@@ -1809,6 +1814,16 @@ auths.oauth2_authURL = Authorize URL
 auths.oauth2_profileURL = Profile URL
 auths.oauth2_emailURL = Email URL
 auths.enable_auto_register = Enable Auto Registration
+auths.sspi_auto_create_users = Automatically create users
+auths.sspi_auto_create_users_helper = Allow SSPI auth method to automatically create new accounts for users that login for the first time
+auths.sspi_auto_activate_users = Automatically activate users
+auths.sspi_auto_activate_users_helper = Allow SSPI auth method to automatically activate new users
+auths.sspi_strip_domain_names = Remove domain names from usernames
+auths.sspi_strip_domain_names_helper = If checked, domain names will be removed from logon names (eg. "DOMAIN\user" and "user@example.org" both will become just "user").
+auths.sspi_separator_replacement = Separator to use instead of \, / and @
+auths.sspi_separator_replacement_helper = The character to use to replace the separators of down-level logon names (eg. the \ in "DOMAIN\user") and user principal names (eg. the @ in "user@example.org").
+auths.sspi_default_language = Default user language
+auths.sspi_default_language_helper = Default language for users automatically created by SSPI auth method. Leave empty if you prefer language to be automatically detected.
 auths.tips = Tips
 auths.tips.oauth2.general = OAuth2 Authentication
 auths.tips.oauth2.general.tip = When registering a new OAuth2 authentication, the callback/redirect URL should be: <host>/user/oauth2/<Authentication Name>/callback
@@ -1834,6 +1849,7 @@ auths.delete_auth_desc = Deleting an authentication source prevents users from u
 auths.still_in_used = The authentication source is still in use. Convert or delete any users using this authentication source first.
 auths.deletion_success = The authentication source has been deleted.
 auths.login_source_exist = The authentication source '%s' already exists.
+auths.login_source_of_type_exist = An authentication source of this type already exists.
 
 config.server_config = Server Configuration
 config.app_name = Site Title