OAuth - Callback URLs

service	callback URL (after the server URL)
bitbucket	`/auth/bitbucket/callback`
facebook	`/auth/facebook/callback`
twitter	`/auth/twitter/callback`
github	`/auth/github/callback`
gitlab	`/auth/gitlab/callback`
mattermost	`/auth/mattermost/callback`
dropbox	`/auth/dropbox/callback`
google	`/auth/google/callback`
saml	`/auth/saml/callback`