/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package org.apache.hc.client5.http.auth;

import java.io.Serializable;
import java.security.Principal;

import org.apache.hc.core5.annotation.Immutable;
import org.ietf.jgss.GSSCredential;

/**
 * {@link Credentials} implementation based on GSSCredential for Kerberos Authentication.
 *
 * @since 4.4
 */
@Immutable
public class KerberosCredentials implements Credentials, Serializable {

    private static final long serialVersionUID = 487421613855550713L;

    /** GSSCredential  */
    private final GSSCredential gssCredential;

    /**
     * Constructor with GSSCredential argument
     *
     * @param gssCredential
     */
    public KerberosCredentials(final GSSCredential gssCredential) {
        this.gssCredential = gssCredential;
    }

    public GSSCredential getGSSCredential() {
        return gssCredential;
    }

    public Principal getUserPrincipal() {
        return null;
    }

    public char[] getPassword() {
        return null;
    }

}

/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */
package org.apache.hc.client5.http.auth;

import java.io.Serializable;
import java.security.Principal;

import org.apache.hc.core5.annotation.Immutable;
import org.ietf.jgss.GSSCredential;

/**
 * {@link Credentials} implementation based on GSSCredential for Kerberos Authentication.
 *
 * @since 4.4
 */
@Immutable
public class KerberosCredentials implements Credentials, Serializable {

    private static final long serialVersionUID = 487421613855550713L;

    /** GSSCredential  */
    private final GSSCredential gssCredential;

    /**
     * Constructor with GSSCredential argument
     *
     * @param gssCredential
     */
    public KerberosCredentials(final GSSCredential gssCredential) {
        this.gssCredential = gssCredential;
    }

    public GSSCredential getGSSCredential() {
        return gssCredential;
    }

    @Override
    public Principal getUserPrincipal() {
        return null;
    }

    @Override
    public char[] getPassword() {
        return null;
    }

}

Add missing '@Override' annotations.