return auth.Credentials{}, false, ErrMissingFields
		}
		ch, s3Err = parseCredentialHeader(authFields[0], region, stype)
		if s3Err != ErrNone {
			return auth.Credentials{}, false, s3Err
		}
	}
	return checkKeyValid(r, ch.accessKey)
}

// parse credentialHeader string into its structured form.
func parseCredentialHeader(credElement string, region string, stype serviceType) (ch credentialHeader, aec APIErrorCode) {