Regarding the official integration with Firebase and the 99-173 error

[Zhen-Bo]

Firebase authentication

After LASENGLE implemented Firebase authentication for FGO logins, the process now includes either an appCheckToken or an appCheckErrorMessage, depending on whether the login environment passes Firebase verification.

• Successful logins include an appCheckToken (a JWT token) in the request form.
• Devices that fail authentication will contain an appCheckErrorMessage, usually indicating issues like inability to find the official Play Store or API authentication failure.

99-173 Error

Concerning the 99-173 error, research conducted on the Rayshift.io Discord Server suggests two potential solutions:

1. Generate a new transfer code by logging in through a device that has passed three Play Integrity API verifications. Subsequently, re-transfer the account and obtain the newly generated account file.
2. Directly log into the account and purchase the least expensive Quartz package for 480 yen. This transaction should resolve the 99-173 issue for the affected account file.

For users with few affected accounts and no access to unrooted devices, the recommended solution is to spend 480 yen to fix the issue. This approach is preferred, as passing the STRONG_INTEGRITY_CHECK requires finding an unbanned keybox.

appCheckToken

Here is the JWT structure of the appCheckToken

{
    "header": {
        "kid": "Q6fyxA",
        "typ": "JWT",
        "alg": "RS256"
    },
    "payload": {
        "app_id": null,
        "issued_at": "${login time}",
        "expires_at": "${login time + 1hr}",
        "token_version": null,
        "debug": false,
        "raw_claims": {
            "sub": "${fixed string by devices?}",
            "aud": ["projects/725677866805", "projects/fategrandorder-46276"],
            "provider": "play_integrity",
            "iss": "https://firebaseappcheck.googleapis.com/725677866805",
            "exp": "${login time + 1hr}",
            "iat": "${login time}",
            "jti": "${generate a unique jti string}"
        }
    },
    "signature": "${RSASHA256('${base64UrlEncode(header)}.${base64UrlEncode(payload)},${public key},${private key}')}"
}

summary

Currently, public and private keys may need to be acquired through hexstr or alternative methods.
The simplest is to directly append an appCheckErrorMessage and include any string or nothing.

[Zhen-Bo]

中文版本:

Firebase authentication

在螺旋社將 FGO 的登入整合至 Firebase 驗證後, 現在的登入 request 表單內會包含 appCheckToken 或 appCheckErrorMessage, 取決於登入環境是否通過 Firebase 驗證。

• 成功登入的 request 會包含 appCheckToken (JWT token)。
• 驗證失敗的裝置會包含 appCheckErrorMessage, 通常表示無法找到正式的 Play 商店或 API 驗證失敗等問題。

99-173 錯誤

關於 99-173 錯誤, 在 Rayshift.io 的 Discord 群中研究出兩個解決方案:

1. 透過已通過三種 Play Integrity API 驗證的裝置登入並產生引繼碼, 使用引繼碼重新轉移帳號並取得新生成的帳號檔案。
2. 直接登入帳號並購買最便宜的 480 日圓的聖晶石。交易成功後可以解決 99-173 的影響。

如果受影響的帳號不多且沒有未 root 的裝置可使用, 建議直接花 480 日圓解決問題。因為要通過 STRONG_INTEGRITY_CHECK 需要找到一個未被封禁的 keybox。 (我兩個受影響帳號都是直接花 480 日圓解決)

appCheckToken

下為 appCheckToken 的 JWT 結構

{
    "header": {
        "kid": "Q6fyxA",
        "typ": "JWT",
        "alg": "RS256"
    },
    "payload": {
        "app_id": null,
        "issued_at": "${login time}",
        "expires_at": "${login time + 1hr}",
        "token_version": null,
        "debug": false,
        "raw_claims": {
            "sub": "${fixed string by devices?}",
            "aud": ["projects/725677866805", "projects/fategrandorder-46276"],
            "provider": "play_integrity",
            "iss": "https://firebaseappcheck.googleapis.com/725677866805",
            "exp": "${login time + 1hr}",
            "iat": "${login time}",
            "jti": "${generate a unique jti string}"
        }
    },
    "signature": "${RSASHA256('${base64UrlEncode(header)}.${base64UrlEncode(payload)},${public key},${private key}')}"
}

結論

目前公鑰和私鑰可能需要透過 hexstr 大佬或其他方法取得。
但是最簡單的方法是直接附加 appCheckErrorMessage 並包含任意字串或是乾脆不要帶任何值。