fix(authentication): OAuth2 authentication url construction

[kon14]

This PR fixes the following issues in regards to OAuth2 authentication url construction:

• code_challenge and code_challenge_method passed as undefined when not explicitly used by provider
• activation url query params not being prefixed by ?

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other (please describe)

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the main branch
• When resolving a specific issue, it's referenced in the PR's description (e.g. fix #xxx, where "xxx" is the issue number)