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(Mono C#) Validate the at_hash Claim of an ID TokenDemonstrates how to hash an access token to compare it with the at_hash claim of an ID token.
// This example requires the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. // This example uses a Google access_token + id_token that looks like this: // { // "access_token": "ya29.a0...0f", // "expires_in": 3599, // "scope": "openid https://www.googleapis.com/auth/userinfo.email", // "token_type": "Bearer", // "id_token": "eyJhb...o5nQ" // } Chilkat.JsonObject jsonToken = new Chilkat.JsonObject(); bool success = jsonToken.LoadFile("qa_data/tokens/google_sample_id_token.json"); if (success == false) { Debug.WriteLine("Failed to load the JSON file..."); return; } // Use Chilkat's JWT API to examine the id_token.. Chilkat.Jwt jwt = new Chilkat.Jwt(); string idToken = jsonToken.StringOf("id_token"); // Extract the JOSE header.. string jose = jwt.GetHeader(idToken); Chilkat.JsonObject jsonHeader = new Chilkat.JsonObject(); jsonHeader.Load(jose); jsonHeader.EmitCompact = false; Debug.WriteLine(jsonHeader.Emit()); // The JOSE header looks like this: // { // "alg": "RS256", // "kid": "e8799db06287515556213c80acbcfd022fb302a9", // "typ": "JWT" // } string claims = jwt.GetPayload(idToken); Chilkat.JsonObject jsonClaims = new Chilkat.JsonObject(); jsonClaims.Load(claims); jsonClaims.EmitCompact = false; Debug.WriteLine(jsonClaims.Emit()); // The claims look like this: // { // "iss": "https://accounts.google.com", // "azp": "258999997753-5ni8lu5f15r7mno97d82f5lir9i9f6i1.apps.googleusercontent.com", // "aud": "258999997753-5ni8lu5f15r7mno97d82f5lir9i9f6i1.apps.googleusercontent.com", // "sub": "111787341816486547572", // "email": "somebody@gmail.com", // "email_verified": true, // "at_hash": "HYJZImlW3mUK-UfjRfXjKw", // "iat": 1615315968, // "exp": 1615319568 // } // The at_hash is the Access Token hash value. Its value is the base64url encoding of the // left-most half of the hash of the octets of the ASCII representation of the access_token value, // where the hash algorithm used is the hash algorithm used in the alg Header Parameter of the // ID Token's JOSE Header. For instance, if the alg is RS256, hash the access_token value with SHA-256, // then take the left-most 128 bits and base64url encode them. The at_hash value is a case sensitive string. string token_to_hash = jsonToken.StringOf("access_token"); string token_hash_expected = jsonClaims.StringOf("at_hash"); // Step 1. hashes the access token using SHA-256 (Google uses `RS256` as the ID Token `alg`). Chilkat.Crypt2 crypt = new Chilkat.Crypt2(); Chilkat.BinData bdHash = new Chilkat.BinData(); crypt.HashAlgorithm = "sha256"; // This encoding mode must match the encoding mode passed in the 2nd arg to AppendEncoded. // The encoding mode can be anything, as long as they are the same in both places. crypt.EncodingMode = "hex"; success = bdHash.AppendEncoded(crypt.HashStringENC(token_to_hash),"hex"); int sz = bdHash.NumBytes; string token_hash_computed = bdHash.GetEncodedChunk(0,sz / 2,"base64url"); // If the hashes are identical, then the access_token as issued for the given id_token. Debug.WriteLine("token_hash_expected: " + token_hash_expected); Debug.WriteLine("token_hash_computed: " + token_hash_computed); |
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