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What each credential proves
These are separate steps in an authentication chain, not interchangeable tokens:
initDatais Telegram’s launch data for the Mini App. Its integrity must be checked on the server before its identity fields are trusted.- An application session is your service’s credential, issued after your backend accepts the validated Telegram identity. It can be a JWT or another session format.
- Telegram Login is a separate OpenID Connect flow. Its
id_tokenis a signed JWT with its own signature and claim-validation requirements; it is not the Mini AppinitDataHMAC flow.
Send raw initData from React
Telegram’s Mini Apps documentation says to load telegram-web-app.js in the document head before other scripts. Once the bridge is available, window.Telegram.WebApp.initData is the string intended for validation. Telegram warns that initDataUnsafe must not be trusted and says data from initData should be used on the bot’s server only after validation.
A React app can POST the raw string to its own backend over HTTPS. Do not treat decoded user fields in the browser as proof of identity, and never put the bot token in client-side code. Client-decoded values can support provisional UI, but authorization and session issuance should wait for backend verification.
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Validate initData on the backend
For the bot-owned verification path, Telegram documents HMAC-SHA-256. The backend reconstructs a data-check string from the received fields, derives a secret from the bot token, and compares the resulting hexadecimal HMAC with the supplied hash.
- Receive the original
initDataquery string. Parse its fields without changing the values needed for verification. - Remove the
hashfield. Sort the remaining fields alphabetically by key, format each askey=value, and join the lines with a line feed to form the data-check string. - Derive the secret key by computing HMAC-SHA-256 over the bot token, using the constant
WebAppDataas the HMAC key. - Compute HMAC-SHA-256 of the data-check string using that derived secret. Encode the result as hexadecimal and compare it with the supplied
hash. Use a constant-time comparison in production code. - Check
auth_dateagainst an explicit maximum age chosen for your application. Reject launch data outside that policy.
The HMAC check establishes integrity; it does not by itself establish freshness. Telegram recommends checking auth_date to prevent outdated launch data from being reused, but does not prescribe a universal age threshold. Choose and document a limit that fits your product’s risk and session experience.
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Issue your application session after validation
Once validation succeeds, map the verified Telegram user identifier to your application’s account model and issue a session under your own security policy. A JWT is one option, not a Telegram requirement. Telegram does not sign a custom application JWT as part of Mini App launch authentication.
If you use a JWT, define its signing keys, issuer, audience, expiry, rotation, and revocation behavior for your application. The backend should issue it only after validating the launch data, and subsequent requests should validate it according to those same application rules.
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Choose the Telegram flow that matches your integration
| Flow | What it authenticates | Who can validate it | Credential or check |
|---|---|---|---|
Mini App initData HMAC |
Telegram launch data and its user identity | Your backend when it owns the bot integration | Bot token; HMAC-SHA-256 verification |
| Third-party Mini App signature | Mini App launch data | A third party that should not receive the bot token | Telegram public key and bot ID; Ed25519 signature verification |
| Telegram Login OIDC | A user authenticated through Telegram Login | Your server | Signed id_token JWT; verify its signature and claims |
| Application session JWT | A session in your own application | Your application’s services | Application-defined signing and validation rules; issued after identity acceptance |
Telegram also documents Ed25519 verification for third parties validating Mini App launch data without the bot token. This is an alternative to the bot-owned HMAC path, not another way to perform that same HMAC check. For Telegram Login’s OIDC flow, validate the id_token signature and claims server-side, including iss (https://oauth.telegram.org), aud (the bot ID), and exp. Telegram’s documented authorization flow also covers state and PKCE; those requirements belong to that Login flow, not automatically to Mini App initData.
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