Merge authentication provider

[dominik003]

Currently we have two different authentication implementations, one for OAuth via azure and a more general variant. The reason for this seems to be that in the case of azure we can use the Microsoft Authentication Library (MSAL) for Python. However, most of the logic between the implementations is duplicated, and there is nothing preventing us from using the more general variant in the Azure case as well. Therefore, we want to merge the two authentication flows and remove any provider-specific details.