Improve error reporting in CAS ticket validation

 src/main/java/org/keycloak/protocol/cas/endpoints/AbstractValidateEndpoint.java

@@ -117,12 +117,13 @@
            userSession = session.sessions().getUserSession(realm, userSessionId);
            if (userSession == null) {
                event.error(Errors.USER_SESSION_NOT_FOUND);
                throw new CASValidationException(CASErrorCode.INVALID_TICKET, "User session not found", Response.Status.BAD_REQUEST);
                throw new CASValidationException(CASErrorCode.INVALID_TICKET, "Code not valid", Response.Status.BAD_REQUEST);
            }
        }

        clientSession = userSession.getAuthenticatedClientSessionByClient(clientUUID);
        if (clientSession == null) {
            event.error(Errors.INVALID_CODE);
            throw new CASValidationException(CASErrorCode.INVALID_TICKET, "Code not valid", Response.Status.BAD_REQUEST);
        }

@@ -131,14 +132,16 @@

        // Either code not available
        if (codeDataSerialized == null) {
            throw new CASValidationException(CASErrorCode.INVALID_TICKET, "Code already used", Response.Status.BAD_REQUEST);
            event.error(Errors.INVALID_CODE);
            throw new CASValidationException(CASErrorCode.INVALID_TICKET, "Code not valid", Response.Status.BAD_REQUEST);
        }

        OAuth2Code codeData = OAuth2Code.deserializeCode(codeDataSerialized);

        String persistedUserSessionId = codeData.getUserSessionId();
        if (!userSessionId.equals(persistedUserSessionId)) {
            throw new CASValidationException(CASErrorCode.INVALID_TICKET, "Code "+codeUUID+"' is bound to a different session", Response.Status.BAD_REQUEST);
            event.error(Errors.INVALID_CODE);
            throw new CASValidationException(CASErrorCode.INVALID_TICKET, "Code not valid", Response.Status.BAD_REQUEST);
        }

        // Finally doublecheck if code is not expired
@@ -173,7 +176,7 @@
        } else {
            if (!client.getClientId().equals(clientSession.getClient().getClientId())) {
                event.error(Errors.INVALID_CODE);
                throw new CASValidationException(CASErrorCode.INVALID_SERVICE, "Auth error", Response.Status.BAD_REQUEST);
                throw new CASValidationException(CASErrorCode.INVALID_SERVICE, "Invalid service", Response.Status.BAD_REQUEST);
            }
        }

@@ -205,7 +208,7 @@
            this.pgtIou = pgtIou;
        } catch (Exception e) {
            event.error(Errors.INVALID_REQUEST);
            throw new CASValidationException(CASErrorCode.PROXY_CALLBACK_ERROR, "Proxy callback return with error", Response.Status.BAD_REQUEST);
            throw new CASValidationException(CASErrorCode.PROXY_CALLBACK_ERROR, "Proxy callback returned an error", Response.Status.BAD_REQUEST);
        }
    }