fix: make redirect URL checking more strict
The OAuth 2.0 Client's Redirect URL and the Redirect URL used in the OAuth 2.0 flow do not check if the query string is equal:
1. Registering a client with allowed redirect URL `https://example.com/callback`
2. Performing OAuth2 flow and requesting redirect URL `https://example.com/callback?bar=foo`
3. Instead of an error, the browser is redirected to `https://example.com/callback?bar=foo` with a potentially successful OAuth2 response.
Additionally, matching Redirect URLs used `strings.ToLower` normalization:
1. Registering a client with allowed redirect URL `https://example.com/callback`
2. Performing OAuth2 flow and requesting redirect URL `https://example.com/CALLBACK`
3. Instead of an error, the browser is redirected to `https://example.com/CALLBACK ` with a potentially successful OAuth2 response.
This patch addresses all of these issues and adds regression tests to keep the implementation secure in future releases.
