feat(auth): allow custom GitLab endpoints for self-managed instances (#6399)

* Allow custom GitLab endpoints for self-hosting

---------

Co-authored-by: Nicolas Giard <github@ngpixel.com>

Author: DerekJarvis

server/modules/authentication/gitlab/authentication.js

@@ -15,6 +15,8 @@ module.exports = {
         clientSecret: conf.clientSecret,
         callbackURL: conf.callbackURL,
         baseURL: conf.baseUrl,
+        authorizationURL: conf.authorizationURL || (conf.baseUrl + '/oauth/authorize'),
+        tokenURL: conf.tokenURL || (conf.baseUrl + '/oauth/token'),
         scope: ['read_user'],
         passReqToCallback: true
       }, async (req, accessToken, refreshToken, profile, cb) => {

server/modules/authentication/gitlab/definition.yml

@@ -24,3 +24,13 @@ props:
     hint: For self-managed GitLab instances, define the base URL (e.g. https://gitlab.example.com). Leave default for GitLab.com SaaS (https://gitlab.com).
     default: https://gitlab.com
     order: 3
+  authorizationURL:
+    type: String
+    title: Authorization URL
+    hint: For self-managed GitLab instances, define an alternate authorization URL (e.g. http://example.com/oauth/authorize). Leave empty otherwise.
+    order: 4
+  tokenURL:
+    type: String
+    title: Token URL
+    hint: For self-managed GitLab instances, define an alternate token URL (e.g. http://example.com/oauth/token). Leave empty otherwise.
+    order: 5