Allow options.assertionConsumerServiceURL or options.callback

[robinbijlani]

Description

Allow AssertionConsumerServiceURL to be provided by options.callback OR options.assertionConsumerServiceURL.

Testing

Describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. If this library has unit and/or integration testing, tests should be added for new functionality and existing tests should complete without errors.

Please include any manual steps for testing end-to-end or functionality not covered by unit/integration tests.

Also include details of the environment this PR was developed in (language/platform/browser version).

• [ ] This change adds test coverage for new/changed/fixed functionality

Checklist

• [ ] I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• [x] All active GitHub checks for tests, formatting, and security are passing
• [x] The correct base branch is being used, if not master