Though this project appears to be dead, I'll post the issue for others who may run into it.

While SRP does not use AWS IAM credentials, if you don't have any in your credential store, the SRP call will fail with a NoCredentialsError exception.

You can create dummy/false credentials, and the call will succeed. Clearly a defect.

For more details (from somebody else, not me) see

https://stackoverflow.com/questions/47849702/aws-boto-warrant-library-srp-authentication-and-credentials-error