// defined parameter to disambiguate the intended IDP in this STS request.
	roleArn := openid.DummyRoleARN
	roleArnStr := r.Form.Get(stsRoleArn)
	if roleArnStr != "" {
		var err error
		roleArn, _, err = globalIAMSys.GetRolePolicy(roleArnStr)
		if err != nil {
			writeSTSErrorResponse(ctx, w, ErrSTSInvalidParameterValue,
				fmt.Errorf("Error processing %s parameter: %v", stsRoleArn, err))
			return
		}
	}