Restructure test data

Currently a lot of test data is repeated in various tests (custom identifier, relying party ID, etc.) We should plan how to keep test data in one place, e.g. have a separate class for user data and another one for relying party data.

Start by locating the tests that repeat custom identifiers, relying party IDs, and other test data. Review how those values are currently defined and compare options for keeping user data and relying party data in separate shared classes. Done means the repository has an agreed restructuring plan for centralizing the repeated data.

Written by the indexing model from the issue text.