Pascal (Lazarus/Delphi)

Verify a JWT Created by the Amazon Cognito Service

See more JSON Web Token (JWT) Examples

Demonstrates how to verify a JWT created by the Amazon Cognito Service. Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.Http,
  Chilkat.StringBuilder,
  Chilkat.Jwt,
  Chilkat.PublicKey,
  Chilkat.JsonObject;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  http: THttp;
  sbJsonKeys: TStringBuilder;
  jsonKeys: TJsonObject;
  jsonKey1: TJsonObject;
  pubKey1: TPublicKey;
  jwt: TJwt;
  token: string;
  sigVerified: Boolean;
  leeway: Integer;
  bTimeValid: Boolean;
  payload: string;
  json: TJsonObject;
  joseHeader: string;

begin
  success := False;

  //  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:

  http := THttp.Create;
  sbJsonKeys := TStringBuilder.Create;
  success := http.QuickGetSb('https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json',sbJsonKeys);
  if (success = False) then
    begin
      WriteLn(http.LastErrorText);
      Exit;
    end;

  jsonKeys := TJsonObject.Create;
  jsonKeys.LoadSb(sbJsonKeys);
  jsonKeys.EmitCompact := False;
  WriteLn(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.
  jsonKey1 := TJsonObject.Create;
  jsonKeys.ObjectOf2('keys[0]',jsonKey1);

  pubKey1 := TPublicKey.Create;
  success := pubKey1.LoadFromString(jsonKey1.Emit());
  if (success = False) then
    begin
      WriteLn(pubKey1.LastErrorText);
      Exit;
    end;

  WriteLn('Success');

  jwt := TJwt.Create;

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

  //  First verify the signature.
  sigVerified := jwt.VerifyJwtPk(token,pubKey1);
  WriteLn('verified: ' + 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.
  leeway := 60;
  bTimeValid := jwt.IsTimeValid(token,leeway);
  WriteLn('time constraints valid: ' + bTimeValid);

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

  //  We can format for human viewing by loading it into Chilkat's JSON object
  //  and emit.
  json := TJsonObject.Create;
  success := json.Load(payload);
  json.EmitCompact := False;
  WriteLn(json.Emit());

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

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


  http.Free;
  sbJsonKeys.Free;
  jsonKeys.Free;
  jsonKey1.Free;
  pubKey1.Free;
  jwt.Free;
  json.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.