(C# UWP/WinRT) Verify a JWT Created by the Amazon Cognito Service

Demonstrates how to verify a JWT created by the Amazon Cognito Service.

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// The public keys for this example are at https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json
// Let's get them:

Chilkat.Http http = new Chilkat.Http();
Chilkat.StringBuilder sbJsonKeys = new Chilkat.StringBuilder();
bool success = await http.QuickGetSbAsync("https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json",sbJsonKeys);
if (success == false) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

Chilkat.JsonObject jsonKeys = new Chilkat.JsonObject();
jsonKeys.LoadSb(sbJsonKeys);
jsonKeys.EmitCompact = false;
Debug.WriteLine(jsonKeys.Emit());

// Here are the keys:

// {
//   "keys": [
//     {
//       "alg": "RS256",
//       "e": "AQAB",
//       "kid": "1A/L5Fsb2EsEwxy5E0cmCMS1BnMe6Jl6NXiMig4iNwU=",
//       "kty": "RSA",
//       "n": "y0w7BJrIJYi ... jKG27z2P3OKw",
//       "use": "sig"
//     },
//     {
//       "alg": "RS256",
//       "e": "AQAB",
//       "kid": "mos6VTJnvDwurY3ghJg6IAPUq+dMwl6CL/iThzJOkzg=",
//       "kty": "RSA",
//       "n": "qbIEH-7tg6yrT ... 3Fj94ooTd0w",
//       "use": "sig"
//     }
//   ]
// }

// Try the 1st key.
Chilkat.JsonObject jsonKey1 = jsonKeys.ObjectOf("keys[0]");
if (jsonKeys.LastMethodSuccess == false) {
    Debug.WriteLine("Did not get the 1st JSON public key.");
    return;
}

Chilkat.PublicKey pubKey1 = new Chilkat.PublicKey();
success = pubKey1.LoadFromString(jsonKey1.Emit());
if (success == false) {
    Debug.WriteLine(pubKey1.LastErrorText);
    return;
}

Debug.WriteLine("Success");

Chilkat.Jwt jwt = new Chilkat.Jwt();

// I did not include the an actual AWS Cognito token here because our test sample used customer-provided data..
string token = "eyJ..asXg";

// First verify the signature.
bool sigVerified = jwt.VerifyJwtPk(token,pubKey1);
Debug.WriteLine("verified: " + Convert.ToString(sigVerified));

// Let's see if the time constraints, if any, are valid.
// The above JWT was created on the afternoon of 16-May-2016, with an expiration of 1 hour.
// If the current system time is before the "nbf" time, or after the "exp" time,
// then IsTimeValid will return false/0.
// Also, we'll allow a leeway of 60 seconds to account for any clock skew.
// Note: If the token has no "nbf" or "exp" claim fields, then IsTimeValid is always true.
int leeway = 60;
bool bTimeValid = jwt.IsTimeValid(token,leeway);
Debug.WriteLine("time constraints valid: " + Convert.ToString(bTimeValid));

// Now let's recover the original claims JSON (the payload).
string payload = jwt.GetPayload(token);
// The payload will likely be in compact form:
Debug.WriteLine(payload);

// We can format for human viewing by loading it into Chilkat's JSON object
// and emit.
Chilkat.JsonObject json = new Chilkat.JsonObject();
success = json.Load(payload);
json.EmitCompact = false;
Debug.WriteLine(json.Emit());

// We can recover the original JOSE header in the same way:
string joseHeader = jwt.GetHeader(token);
// The payload will likely be in compact form:
Debug.WriteLine(joseHeader);

// We can format for human viewing by loading it into Chilkat's JSON object
// and emit.
success = json.Load(joseHeader);
json.EmitCompact = false;
Debug.WriteLine(json.Emit());