add hdb_get_realms

lib/hdb/hdb.h

@@ -193,6 +193,13 @@ typedef struct HDB{
      * point for the module.
      */
     krb5_error_code (*hdb_destroy)(krb5_context, struct HDB*);
+    /**
+     * Get the list of realms this backend handles.
+     * This call is optional to support. The returned realms are used
+     * for announcing the realms over bonjour. Free returned array
+     * with krb5_free_host_realm().
+     */
+    krb5_error_code (*hdb_get_realms)(krb5_context, struct HDB *, krb5_realm **);
     /**
      * Change password.
      *