feat: Improve oauth redirect (#303)

* fix: redirects after oauth can potentially misalign with server's actually hostname

* feat: remove `RedirectURL` from oauth config, as it should checked by provider rather than client

* feat: align oauth endpoint with the hostname in requests

docs/admin/admin_swagger.yaml

@@ -143,15 +143,12 @@ definitions:
         type: boolean
       pkce_method:
         type: string
-      redirect_url:
-        type: string
       scopes:
         type: string
     required:
     - client_id
     - client_secret
     - oauth_type
-    - redirect_url
     type: object
   admin.PeerBatchDeleteForm:
     properties:
@@ -611,8 +608,6 @@ definitions:
         type: boolean
       pkce_method:
         type: string
-      redirect_url:
-        type: string
       scopes:
         type: string
       updated_at: