Add support for basic authentication

src/main/java/org/gitlab4j/api/GitLabApi.java

@@ -528,6 +528,18 @@ public GitLabApi withRequestResponseLogging(Logger logger, Level level) {
         return (this);
     }
 
+
+    /**
+     * Enable basic authentication when connecting to the gitlab server.
+     *
+     * @param userName the user name
+     * @param password the password
+     */
+    public GitLabApi enableBasicAuthentication(String userName, String password) {
+        apiClient.enableBasicAuthentication(userName, password);
+        return (this);
+    }
+
     /**
      * Enable the logging of the requests to and the responses from the GitLab server API
      * using the GitLab4J shared Logger instance and Level.FINE as the level.

src/main/java/org/gitlab4j/api/GitLabApiClient.java

@@ -68,6 +68,9 @@ public class GitLabApiClient implements AutoCloseable {
     private Integer sudoAsId;
     private Integer connectTimeout;
     private Integer readTimeout;
+    private boolean basicAuthIsEnabled = false;
+    private String basicAuthUserName;
+    private String basicAuthPassword;
 
     /**
      * Construct an instance to communicate with a GitLab API server using the specified GitLab API version,
@@ -255,6 +258,18 @@ public void close() {
         }
     }
 
+    /**
+     * Enable basic authentication
+     *
+     * @param userName the user name
+     * @param password the password
+     */
+    void enableBasicAuthentication(String userName, String password) {
+        basicAuthIsEnabled = true;
+        basicAuthUserName = userName;
+        basicAuthPassword = password;
+    }
+
     /**
      * Enable the logging of the requests to and the responses from the GitLab server API.
      *
@@ -799,6 +814,12 @@ protected Invocation.Builder invocation(URL url, MultivaluedMap<String, String>
         } else {
             builder = builder.header(authHeader, authValue).accept(accept);
         }
+        /* For servers with basic authentication enabled. */
+        if (basicAuthIsEnabled) {
+            String rawString = basicAuthUserName + ":" + basicAuthPassword;
+            String headerValue = "Basic " + java.util.Base64.getEncoder().encodeToString(rawString.getBytes());
+            builder.header(AUTHORIZATION_HEADER, headerValue);
+        }
 
         // If sudo as ID is set add the Sudo header
         if (sudoAsId != null && sudoAsId.intValue() > 0)