Make `source` param required while calling the server endpoint. ([[ https://linear.app/comm/issue/ENG-1870/make-source-a-required-parameter-to-login-function-in-lib | task ]])
Note: there are still some places where `source` is optional but it is used in a different context - for now we care only about making it required while connecting with the keyserver, but if it is signification can be refactored in the future to make `source` required in remaining places.