Display more specific error message when non-optional attributes are missing + fix typo

internal/servercore/api.go

@@ -190,16 +190,16 @@ func (s *Server) StartSession(req interface{}) (*irma.Qr, string, error) {
 	request := rrequest.SessionRequest()
 	action := request.Action()
 
-	if err := s.validateRequest(request); err != nil {
-		return nil, "", err
-	}
-
 	if action == irma.ActionIssuing {
 		if err := s.validateIssuanceRequest(request.(*irma.IssuanceRequest)); err != nil {
 			return nil, "", err
 		}
 	}
 
+	if err := s.validateRequest(request); err != nil {
+		return nil, "", err
+	}
+
 	session := s.newSession(action, rrequest)
 	s.conf.Logger.WithFields(logrus.Fields{"action": action, "session": session.token}).Infof("Session started")
 	if s.conf.Logger.IsLevelEnabled(logrus.DebugLevel) {

requests.go

@@ -487,7 +487,7 @@ func (cr *CredentialRequest) Validate(conf *Configuration) error {
 			}
 		}
 		if !found {
-			return errors.New("Credential request contaiins unknown attribute")
+			return errors.New("Credential request contains unknown attribute")
 		}
 	}