Authentication flows

[Thechi2000]

We need to allow authentication through two methods:

• An admin token to manage events using a single shared token. (b43140e)
• Microsoft Entra ID, for the users, ref: https://learn.microsoft.com/en-us/entra/identity/
  • Dummy user sessions (for dev only)

[Thechi2000]

I've discussed with some people from the DSI from EPFL, and it turns out that the new SSO (Microsoft Entra) will be available by the end of the summer. Thus, we can skip Tequila and directly implement it. In the meantime, we may want to add a dummy login button to emulate a user session.