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(Unicode 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.
#include <C_CkJsonObjectW.h> #include <C_CkJwtW.h> #include <C_CkCrypt2W.h> #include <C_CkBinDataW.h> void ChilkatSample(void) { HCkJsonObjectW jsonToken; BOOL success; HCkJwtW jwt; const wchar_t *idToken; const wchar_t *jose; HCkJsonObjectW jsonHeader; const wchar_t *claims; HCkJsonObjectW jsonClaims; const wchar_t *token_to_hash; const wchar_t *token_hash_expected; HCkCrypt2W crypt; HCkBinDataW bdHash; int sz; const wchar_t *token_hash_computed; // 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" // } jsonToken = CkJsonObjectW_Create(); success = CkJsonObjectW_LoadFile(jsonToken,L"qa_data/tokens/google_sample_id_token.json"); if (success == FALSE) { wprintf(L"Failed to load the JSON file...\n"); CkJsonObjectW_Dispose(jsonToken); return; } // Use Chilkat's JWT API to examine the id_token.. jwt = CkJwtW_Create(); idToken = CkJsonObjectW_stringOf(jsonToken,L"id_token"); // Extract the JOSE header.. jose = CkJwtW_getHeader(jwt,idToken); jsonHeader = CkJsonObjectW_Create(); CkJsonObjectW_Load(jsonHeader,jose); CkJsonObjectW_putEmitCompact(jsonHeader,FALSE); wprintf(L"%s\n",CkJsonObjectW_emit(jsonHeader)); // The JOSE header looks like this: // { // "alg": "RS256", // "kid": "e8799db06287515556213c80acbcfd022fb302a9", // "typ": "JWT" // } claims = CkJwtW_getPayload(jwt,idToken); jsonClaims = CkJsonObjectW_Create(); CkJsonObjectW_Load(jsonClaims,claims); CkJsonObjectW_putEmitCompact(jsonClaims,FALSE); wprintf(L"%s\n",CkJsonObjectW_emit(jsonClaims)); // 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. token_to_hash = CkJsonObjectW_stringOf(jsonToken,L"access_token"); token_hash_expected = CkJsonObjectW_stringOf(jsonClaims,L"at_hash"); // Step 1. hashes the access token using SHA-256 (Google uses `RS256` as the ID Token `alg`). crypt = CkCrypt2W_Create(); bdHash = CkBinDataW_Create(); CkCrypt2W_putHashAlgorithm(crypt,L"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. CkCrypt2W_putEncodingMode(crypt,L"hex"); success = CkBinDataW_AppendEncoded(bdHash,CkCrypt2W_hashStringENC(crypt,token_to_hash),L"hex"); sz = CkBinDataW_getNumBytes(bdHash); token_hash_computed = CkBinDataW_getEncodedChunk(bdHash,0,sz / 2,L"base64url"); // If the hashes are identical, then the access_token as issued for the given id_token. wprintf(L"token_hash_expected: %s\n",token_hash_expected); wprintf(L"token_hash_computed: %s\n",token_hash_computed); CkJsonObjectW_Dispose(jsonToken); CkJwtW_Dispose(jwt); CkJsonObjectW_Dispose(jsonHeader); CkJsonObjectW_Dispose(jsonClaims); CkCrypt2W_Dispose(crypt); CkBinDataW_Dispose(bdHash); } |
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