Update PIConstants.java

Author: lukasmatusiewicz

src/main/java/org/privacyidea/PIConstants.java

@@ -50,6 +50,7 @@ private PIConstants()
     public static final String PASSWORD = "password";
     public static final String PASS = "pass";
     public static final String SERIAL = "serial";
+    public static final String CHALLENGE_STATUS = "challenge_status";
     public static final String TYPE = "type";
     public static final String TRANSACTION_ID = "transaction_id";
     public static final String REALM = "realm";