Support login using OAuth 2.0 in ownCloud

[dkocher]

There is a plugin for ownCloud adding login using OAuth2.

https://github.com/owncloud/oauth2

This app implements the OAuth 2.0 Authorization Code Flow.

[dkocher]

This should be quite straight forward however we need a way to allow users to enter the client_id from registration details.

First the clients have to be registered in the admin settings: /index.php/settings/admin?sectionid=additional#oauth2