Validate SAML parameters before doing AssumeRoleWithSAML
Validate SAML parameters before doing AssumeRoleWithSAML

Check that we have something resembling a value in the SAMLAssertion
and PrincipalARN before making the AssumeRole call.  We'll leave the
data validation to AWS, but make sure we provide a more helpful error
message in case these values aren't set.

mmmorris1975/aws-runas,mmmorris1975/aws-runas,mmmorris1975/aws-runas,mmmorris1975/aws-runas,mmmorris1975/aws-runas