public String getDefaultApiAuthenticatedUser() {
    return properties.getProperty(API_AUTHENTICATED_USER.getKey());
  }
Gets the username of the default user assumed to be executing API calls.
<p/>
If this value is <code>null</code> or empty then no default user is set and one must be
specified when issuing API calls.

@return the username of a user.
ambari-server/src/main/java/org/apache/ambari/server/configuration/Configuration.java