Prerequisites

• Feature: Add multi provider authentication  ontologies_api#41
• Feature: Add multi provider authentification ontologies_linked_data#95

Context

See ontoportal/ontoportal-project#26. and lifewatch-eric/ontologies_linked_data#5

This PR adds login using external authentication providers Github, Google, Orcid, and Keycloak. It was implemented using the omni_auth gem that standardizes multi-provider authentication for web applications.

The general workflow is so

1. Redirect the user to the external provider to connect.
2. The external provider returns a token authenticating the user.
3. The UI sends the token and the provider name (e.g. Github) to the API.
4. The API test that the token is valid by two possible ways, by trying to decode the token using a secret key or by calling again the external provider.
5. If the token is valid the external provider returns the user information (name, email, ....)
6. With the email we check if we find an existent user with the same email otherwise we create a new one with the date received.
7. If connected using Github or ORCID, we synchronize the user githhubId and orcidId attributes.

Changes

• Install and configure omniauth gems (c3be314)
• Add a helper to get omniauth_providers details (70cb7ce)
• Add external auth providers icons on the login in page (fa9f56d)
• Add OAuth login action (69a17c7)
• Add omniauth_token_provider helper (5a8f1a2)