AuthClientSubsystem: HTTP Login and Server Select

UAuthClientSubsystem is a UGameInstanceSubsystem that owns every interaction with the ASP.NET Core AuthServer. It is responsible for registering and authenticating accounts, fetching the list of available game servers, selecting a server to play on, and storing the resulting tokens and connection details that UGameClientSubsystem needs to open a TCP game connection. No IOCP GameServer communication is performed by this class — that boundary is enforced by design.

Class declaration

UCLASS()
class MMOCLIENT1_API UAuthClientSubsystem : public UGameInstanceSubsystem
{
    GENERATED_BODY()
public:
    UPROPERTY(BlueprintAssignable, Category = "Auth")
    FAuthClientResult OnRegisterResult;

    UPROPERTY(BlueprintAssignable, Category = "Auth")
    FAuthClientResult OnLoginResult;

    UPROPERTY(BlueprintAssignable, Category = "Auth")
    FAuthServerListResult OnServerListResult;

    UPROPERTY(BlueprintAssignable, Category = "Auth")
    FAuthSelectServerResult OnSelectServerResult;

    UFUNCTION(BlueprintCallable, Category = "Auth")
    void SetAuthServerBaseUrl(const FString& InBaseUrl);

    UFUNCTION(BlueprintPure, Category = "Auth")
    FString GetAuthServerBaseUrl() const;

    UFUNCTION(BlueprintCallable, Category = "Auth")
    bool Register(const FString& Account, const FString& Password, const FString& Nickname);

    UFUNCTION(BlueprintCallable, Category = "Auth")
    bool Login(const FString& Account, const FString& Password);

    UFUNCTION(BlueprintCallable, Category = "Auth")
    bool RequestServerList();

    UFUNCTION(BlueprintCallable, Category = "Auth")
    bool SelectServer(int32 ServerId);

    UFUNCTION(BlueprintCallable, Category = "Auth")
    bool SelectDefaultServer();

    UFUNCTION(BlueprintCallable, Category = "Auth")
    void ClearLocalSession();

    // BlueprintPure getters: IsLoggedIn, GetAccessToken, GetEnterToken,
    // GetSelectedCharacterId, GetSelectedGameServerIp, GetSelectedGameServerPort,
    // GetCachedServerList, GetAuthServerBaseUrl
};

The default AuthServerBaseUrl is http://127.0.0.1:5000. Change it at runtime with SetAuthServerBaseUrl before making any requests, or configure it via EditAnywhere in the Blueprint defaults.

HTTP request internals

All requests are made through Unreal’s FHttpModule. JSON POST requests are sent via the private helper SendJsonRequest, and GET requests via SendGetRequest. Both helpers:

Build the full URL by concatenating AuthServerBaseUrl and a route string (e.g. /auth/login).
Create a request via FHttpModule::Get().CreateRequest().
Set Accept: application/json and Content-Type: application/json.
Attach a completion delegate that is invoked on the game thread when the response arrives.
Call ProcessRequest() and return its success flag.

If ProcessRequest() returns false, the corresponding OnXxxResult delegate is broadcast immediately with bSuccess = false.

Methods

`Register`

Creates a new player account on the AuthServer.

Account

FString

required

The player’s account identifier (typically an email address).

Password

FString

required

The desired account password.

Nickname

FString

required

The in-game display name for the new account.

HTTP request:

POST /auth/register
{
  "account": "player@example.com",
  "password": "secret",
  "nickname": "PlayerOne"
}

Response handling: The JSON response is parsed for success (bool) and message (string). The result is broadcast on OnRegisterResult(bSuccess, Message). Registration does not store an access token — a separate login call is required.

Authenticates an existing account and stores the returned accessToken.

Account

FString

required

The registered account identifier.

Password

FString

required

The account password.

HTTP request:

POST /auth/login
{
  "account": "player@example.com",
  "password": "secret"
}

Response handling: On success, the accessToken field is extracted from the JSON response and stored in the private AccessToken member. On failure, AccessToken, EnterToken, SelectedGameServerIp, and SelectedGameServerPort are all cleared. The result is broadcast on OnLoginResult(bSuccess, Message).

`RequestServerList`

Fetches the list of available game servers. No authentication header is required — the server list is publicly accessible. HTTP request:

GET /servers

Response handling: The response body is a JSON array. Each element is parsed into an FAuthServerInfo struct:

USTRUCT(BlueprintType)
struct FAuthServerInfo
{
    int32  ServerId;
    FString Name;
    FString Ip;
    int32  Port;
    int32  CurrentUsers;
    int32  MaxUsers;
    bool   bMaintenance;
};

The parsed array is stored in CachedServerList and broadcast on OnServerListResult(bSuccess, Servers). If parsing fails, CachedServerList is left empty.

`SelectServer`

Exchanges the stored AccessToken and a ServerId for a short-lived EnterToken, plus the game server IP and port.

ServerId

int32

required

The ServerId of the server to connect to, as returned by RequestServerList.

Precondition: AccessToken must be non-empty (i.e. Login must have succeeded). If it is empty, OnSelectServerResult is broadcast immediately with bSuccess = false and the message "login required". HTTP request:

POST /auth/select-server
{
  "accessToken": "<jwt>",
  "serverId": 1
}

Response handling: On success, the following fields are extracted and stored:

JSON field	Stored in
`gameServerIp`	`SelectedGameServerIp`
`gameServerPort`	`SelectedGameServerPort`
`enterToken`	`EnterToken`
`characterId`	`SelectedCharacterId`

On failure, all four fields are reset to empty/zero. The result is broadcast on OnSelectServerResult(bSuccess, GameServerIp, GameServerPort, EnterToken, CharacterId, Message).

`SelectDefaultServer`

Convenience wrapper that calls SelectServer with the first non-maintenance server from CachedServerList. If CachedServerList is empty or all servers are in maintenance, it broadcasts OnSelectServerResult with bSuccess = false and "no available server".

`ClearLocalSession`

Resets all stored session state: AccessToken, EnterToken, SelectedGameServerIp, SelectedGameServerPort, SelectedCharacterId, and CachedServerList. Call this on logout or when returning to the login screen.

Stored state

After a successful Login → RequestServerList → SelectServer sequence, the following accessors return valid values:

Accessor	Type	Description
`GetAccessToken()`	`FString`	JWT used to authenticate subsequent AuthServer requests
`GetEnterToken()`	`FString`	Short-lived token passed to `GameClientSubsystem::ConnectAndEnterGame`
`GetSelectedGameServerIp()`	`FString`	IP address of the chosen game server
`GetSelectedGameServerPort()`	`int32`	TCP port of the chosen game server
`GetSelectedCharacterId()`	`int64`	Character ID associated with the selected server slot
`GetCachedServerList()`	`TArray<FAuthServerInfo>`	All servers returned by the last `RequestServerList` call
`IsLoggedIn()`	`bool`	Returns `true` when `AccessToken` is non-empty

Delegates

// Fired by Register and Login
DECLARE_DYNAMIC_MULTICAST_DELEGATE_TwoParams(
    FAuthClientResult,
    bool, bSuccess,
    const FString&, Message);

// Fired by RequestServerList
DECLARE_DYNAMIC_MULTICAST_DELEGATE_TwoParams(
    FAuthServerListResult,
    bool, bSuccess,
    const TArray<FAuthServerInfo>&, Servers);

// Fired by SelectServer / SelectDefaultServer
DECLARE_DYNAMIC_MULTICAST_DELEGATE_SixParams(
    FAuthSelectServerResult,
    bool, bSuccess,
    const FString&, GameServerIp,
    int32, GameServerPort,
    const FString&, EnterToken,
    int64, CharacterId,
    const FString&, Message);

Always call SelectServer (or SelectDefaultServer) before calling UGameClientSubsystem::ConnectAndEnterGame. The game subsystem requires the EnterToken, SelectedGameServerIp, and SelectedGameServerPort that are only available after a successful SelectServer response. ALoginPlayerController retrieves them via GetAuthSubsystem()->GetEnterToken() and friends inside its HandleSelectServerResult callback.

UE5 Client

AuthClientSubsystem: HTTP Login and Server Select

Class declaration

HTTP request internals

Methods

`Register`

`RequestServerList`

`SelectServer`

`SelectDefaultServer`

`ClearLocalSession`

Stored state

Delegates

Build docs developers (and LLMs) love

UE5 Client

Documentation Index

​Class declaration

​HTTP request internals

​Methods

​Register

​Login

​RequestServerList

​SelectServer

​SelectDefaultServer

​ClearLocalSession

​Stored state

​Delegates

Build docs developers (and LLMs) love

Class declaration

HTTP request internals

Methods

`Register`

`Login`

`RequestServerList`

`SelectServer`

`SelectDefaultServer`

`ClearLocalSession`

Stored state

Delegates