support dynamic client registration

[butonic]

We currently hardcoded the default client identifiers for openid connect because lico disabled it by default: #2026

When trying to develop a new client for ocis developers would like to use OpenID Connect Dynamic Client Registration OOTB.

[butonic]

It is possible to enable dynamic client registration by setting IDP_ALLOW_DYNAMIC_CLIENT_REGISTRATION=true. But when testing with our clients we encountered some problems. Maybe @michaelstingl can elaborate.

[butonic]

There is a huge docs issue trying to sort out what should be documented: owncloud/docs#3499

[butonic]

The problems seem to have been caused by the client registration expiring after an hour. They no longer expire, but this can be reenabled by setting IDP_DYNAMIC_CLIENT_SECRET_DURATION if desired.

[michaelstingl]

Desktop + mobile apps DCR when announced in /.well-known/openid-configuration, and when it fails, they fall back to client id + secret.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 10 days if no further activity occurs. Thank you for your contributions.

[micbar]

DCR works with the example ocis deployment.