Receving error: The authorization server does not support this response type.

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After integrating phabricator-gitlab-auth-provider (with minor code change) into Phabricator, I'm getting "The authorization server does not support this response type." and did not redirect to Phabricator. Not sure what is wrong. Any help is highly appreciated.

Steps I did -

1. Installed Phabricator in VirtualBox and exposed it via IP address 10.208.14.152.
2. Create a gitlab OAuth client in my Dev account, all scopes are enabled.
   
3. Downloaded https://github.com/manGoweb/phabricator-gitlab-auth-provider/blob/master/src/oauth/PhabricatorGitlabAuthProvider.php and https://github.com/manGoweb/phabricator-gitlab-auth-provider/blob/master/src/oauth/PhutilGitlabAuthAdapter.php. Replaced all occurance of mangoweb.org to gitlab.com.
4. Placed both files mentioned above into VirtualBox's /apps/phabricator/phabricator/src/applications/auth/provider
5. from /apps/phabricator, ran ./phabricator/arcanist/bin/arc liberate /apps/phabricator/. Ensured
   the phutil_library_map.php is updated with two new files added in step#3 above. My phutil_library_init.php did not changed, and is -
   
6. Activated Gitlab authentication in Phabricator -
   
7. Restarted httpd service
8. Login to Phabricator via Gitlab using my Test account and I get error "The authorization server does not support this response type.". Screenshot in each steps are below -
   

Not sure what I am doing wrong here. Please advise.