Fix 500 error when user has no data access token

[Gautam-aman]

Problem

Calling getDataAccessToken for a user with no existing data access tokens
throws an IndexOutOfBoundsException, resulting in a 500 response.

Solution

Guard against an empty token list and create a new data access token
when none exists.

Impact

Prevents server error and aligns behavior with expected token lifecycle.

Tests

• mvn test -Dtest=UuidDataAccessTokenServiceImplTest

Fixes #11905

[sachindigharra]

Issue: The user is still logged into the system but doesn’t have a token to access resources.
Solution: Since the user is already verified, we should generate and store a token instead of re-verifying. This ensures that future resource access is not interrupted.

[Gautam-aman]

Yes, exactly this change ensures that already-authenticated users receive
a newly generated and persisted data access token when none exists, avoiding
re-verification and preventing 500 errors on resource access.