Pascal (Lazarus/Delphi)

Verify JWT Using HS256, HS384, or HS512

See more JSON Web Token (JWT) Examples

Demonstrates how to verify a JWT that was signed using HS256, HS384, or HS512. (HS256 is JWT's acronym for HMAC-SHA256.)

This example verifies the signature. It also does the following:

• Checks to see if the time constraints ("nbf" and "exp") are valid.
• Recovers the original JOSE header.
• Recovers the original claims JSON.

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.JsonObject,
  Chilkat.Jwt;

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

procedure RunDemo;
var
  success: Boolean;
  jwt: TJwt;
  token: string;
  sigVerified: Boolean;
  leeway: Integer;
  bTimeValid: Boolean;
  payload: string;
  json: TJsonObject;
  joseHeader: string;

begin
  success := False;

  //  Demonstrates how to verify an HMAC JWT using a shared secret (password).

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

  jwt := TJwt.Create;

  token := 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRwOi8vZXhhbXBsZS5vcmciLCJzdWIiOiJKb2huIiwiYXVkIjoiaHR0cDovL2V4YW1wbGUuY29tIiwiaWF0IjoxNDYzNDMxODEyLCJuYmYiOjE0NjM0MzE4MTIsImV4cCI6MTQ2MzQzNTQxMn0.SHnMJ11qJH5pbp22YchT_9fL2HIx0koHiUHLG67_foU';

  //  First verify the signature.
  //  The password used to create this JWT was "secret".
  sigVerified := jwt.VerifyJwt(token,'secret');
  WriteLn('with correct password: ' + sigVerified);

  //  Now try with a different password:
  sigVerified := jwt.VerifyJwt(token,'secret2');
  WriteLn('with incorrect password ' + 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());


  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.