Fix compilation with Erlang/OTP 27: don't use the reserved word 'maybe'

src/ejabberd_auth.erl

@@ -425,7 +425,7 @@ user_exists(User, Server) ->
 	    false
     end.
 
--spec user_exists_in_other_modules(atom(), binary(), binary()) -> boolean() | maybe.
+-spec user_exists_in_other_modules(atom(), binary(), binary()) -> boolean() | maybe_exists.
 user_exists_in_other_modules(Module, User, Server) ->
     user_exists_in_other_modules_loop(
       auth_modules(Server) -- [Module], User, Server).
@@ -439,7 +439,7 @@ user_exists_in_other_modules_loop([AuthModule | AuthModules], User, Server) ->
 	{false, _} ->
 	    user_exists_in_other_modules_loop(AuthModules, User, Server);
 	{{error, _}, _} ->
-	    maybe
+	    maybe_exists
     end.
 
 -spec which_users_exists(list({binary(), binary()})) -> list({binary(), binary()}).

src/ejabberd_auth_anonymous.erl

@@ -153,7 +153,7 @@ check_password(User, _AuthzId, Server, _Password) ->
 	 %% If user exists in other module, reject anonnymous authentication
 	 true -> false;
 	 %% If we are not sure whether the user exists in other module, reject anon auth
-	 maybe -> false;
+	 maybe_exists -> false;
 	 false -> login(User, Server)
      end}.