Limit this plugin to ORCID; transition the generic use-case to OpenID

[ctgraham]

This plugin was to head in the direction of being a generic tool for OAuth-2.0-based authentication. This is probably unnecessarily complex.

This OAuth 2.0 based authentication is valuable for login via ORCID credentials, as ORCID.org does not support OpenID, at least not yet.

OpenID is designed to do just authentication, whereas OAuth provides authentication services as part of granting larger API access. Since we probably won't need broader API access outside of possible use cases for ORCID, defer other authentication types (Microsoft, Google, Yahoo!, etc) to OpenID instead.

[asmecher]

Are you sure that's still accurate? ORCID does now seem to support OpenID since 2018. https://info.orcid.org/orcid-openid-connect-and-implicit-authentication/