login: use Invenio user to login into REANA

[diegodelemos]

Currently, we have Invenio working inside the REANA-Server. This means we have the Invenio user available. This will be the user used to login into REANA.

In order to login into REANA we shall use the CERN SSO. More information, from generic to more CERN specific here:

• The OAuth2 workflow (diagram)
• OAuth2 workflow with Invenio/GitHub on a small example app https://github.com/inveniosoftware/invenio-oauthclient/blob/master/examples/github_app.py
  • Docs on how to run it in the docstring
• How to run the OAuth2 workflow locally at CERN https://digital-repositories.web.cern.ch/digital-repositories/common-recipes/cern-oauth/

Once the user is authenticated, we should use the same procedure as in https://github.com/reanahub/reana-server/pull/148/files#diff-280a2a9344a69bb67263b622356572f0R284, using flask_jwt_extended to set the relevant cookies.

Once the user is logged we should protect the [REANA-Server endpoints](https://github.com/reanahub/reana-server/tree/api-login/reana_server/rest.

Note: The REANA user is different than the Invenio user, but we do not care right now since we first focus on login with OAuth. This will be taken care of by #152.

[diegodelemos]

Closed by #157.