Return Auth/Config Error in PayPalClient

[sarahkoop]

Summary of changes

• Propagate errors fetching configuration (which propagates authorization errors under the hood) to PayPalListener when auth is invalid or config is unable to be fetched, rather than returning a generic error message that PayPal is not enabled.
• Note: This will return the merchant's own auth error defined in their ClientTokenProvider if an error is thrown at that level, or will propagate config fetching errors or other auth errors (ex if ClientTokenProvider is null).
• Fixes Calling onFailure Results Exception Stating Paypal is Not Enabled #821

Checklist

• Added a changelog entry

Authors

• @sarahkoop

[sarahkoop]

Would we prefer to wrap the merchant's error defined in ClientTokenProvider with our own error message, or just propagate it back to them? Wrapping the error would have implications across the entire SDK if we changed BraintreeClient or AuthorizationLoader implementation,.

[tdchow]

Would we prefer to wrap the merchant's error defined in ClientTokenProvider with our own error message, or just propagate it back to them? Wrapping the error would have implications across the entire SDK if we changed BraintreeClient or AuthorizationLoader implementation,.

It might reduce merchant debug time if we just propagate the same exception. If we were to wrap the error, the merchant would need to go one level deep in the stacktrace to see that it was their error in the ClientTokenProvider.