... as discussed in [Issue 507](https://github.com/openstreetmap/operations/issues/507)
and described by @mmd-osm.
To activate, set the value of `doorkeeper_signing_key` to RSA private key.
Allows using openstreetmap as an identity provider.
Adds `openid` scope to OAuth2 authorizations, required to login to OSM.
Currently, the only claims returned are:
- "openid" scope: "sub" and "preferred_username"
- "read_email" scope: "email"
