(Delphi DLL) Verify JWT Using an RSA Public Key (RS256, RS384, RS512)

Demonstrates how to verify a JWT that was signed using an RSA private key.

This example verifies the RSA 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.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Jwt, PublicKey, JsonObject;

...

procedure TForm1.Button1Click(Sender: TObject);
var
pubKey: HCkPublicKey;
success: Boolean;
jwt: HCkJwt;
token: PWideChar;
sigVerified: Boolean;
leeway: Integer;
bTimeValid: Boolean;
payload: PWideChar;
json: HCkJsonObject;
joseHeader: PWideChar;

begin
// Demonstrates how to verify an JWT using an RSA public key.

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

pubKey := CkPublicKey_Create();
success := CkPublicKey_LoadFromFile(pubKey,'qa_data/pem/rsa_public.pem');

jwt := CkJwt_Create();

token := 'eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRwOi8vZXhhbXBsZS5vcmciLCJzdWIiOiJKb2huIiwiYXVkIjoiaHR0cDovL2V4YW1wbGUuY29tIiwiaWF0IjoxNDYzNDQ1MjM4LCJuYmYiOjE0NjM0NDUyMzgsImV4cCI6MTQ2MzQ0ODgzOH0.XRtqed6nuJ9lrp0wbNdDX3fCkSh_d9cHAniPbNcqm7G-5N3mtI5ntQvZBDP3pHtECVqufuDwW7XgUtzAi0ZXhyiRm1iZ3wMSN5lHWv52OQJmMHPA7VPd8Q1hDG-tx-QswzJKd75OEUHP7wIXq2Mg_YVElfDvJI6TGjGyS1y-RLHlz-ldlGsEwIBkO0PtzIYTVov97x8p9KCsPNhS4lZUIqKOYoTZUV5LpuAWARl-636DfMEB_A5_IEaw_W8leh2suP2ULVZxwE-Tk1kBC9tsSGrBrPTtg7sziaV4Lbb0JRANmh98uTRu5f8ji9CVOnpbMiAzjsJSy56kz_olweXSuA';

// First verify the signature.
sigVerified := CkJwt_VerifyJwtPk(jwt,token,pubKey);
Memo1.Lines.Add('verified: ' + IntToStr(Ord(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 := CkJwt_IsTimeValid(jwt,token,leeway);
Memo1.Lines.Add('time constraints valid: ' + IntToStr(Ord(bTimeValid)));

// Now let's recover the original claims JSON (the payload).
payload := CkJwt__getPayload(jwt,token);
// The payload will likely be in compact form:
Memo1.Lines.Add(payload);

// We can format for human viewing by loading it into Chilkat's JSON object
// and emit.
json := CkJsonObject_Create();
success := CkJsonObject_Load(json,payload);
CkJsonObject_putEmitCompact(json,False);
Memo1.Lines.Add(CkJsonObject__emit(json));

// We can recover the original JOSE header in the same way:
joseHeader := CkJwt__getHeader(jwt,token);
// The payload will likely be in compact form:
Memo1.Lines.Add(joseHeader);

// We can format for human viewing by loading it into Chilkat's JSON object
// and emit.
success := CkJsonObject_Load(json,joseHeader);
CkJsonObject_putEmitCompact(json,False);
Memo1.Lines.Add(CkJsonObject__emit(json));

CkPublicKey_Dispose(pubKey);
CkJwt_Dispose(jwt);
CkJsonObject_Dispose(json);

end;