code: func (m *signingMethodNone) Verify(signingString, signature string, key interface{}) (err error) {
  	// Key must be UnsafeAllowNoneSignatureType to prevent accidentally
  	// accepting 'none' signing method
  	if _, ok := key.(unsafeNoneMagicConstant); !ok {
  		return NoneSignatureTypeDisallowedError
  	}
  	// If signing method is none, signature must be an empty string
  	if signature != "" {
  		return NewValidationError(
  			"'none' signing method with non-empty signature",
  			ValidationErrorSignatureInvalid,
  		)
  	}
  
  	// Accept 'none' signing method.
  	return nil
  }
docs: // Only allow 'none' alg type if UnsafeAllowNoneSignatureType is specified as the key