(Delphi ActiveX) OAuth2 Token using IdentityServer4 with Client Credentials

Demonstrates how to get an OAuth2 access token using the client credential flow with IdentityServer4.

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

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

...

procedure TForm1.Button1Click(Sender: TObject);
var
http: TChilkatHttp;
resp: IChilkatHttpResponse;
json: TChilkatJsonObject;
success: Integer;
tokenEndpoint: WideString;
grantTypes: IChilkatJsonArray;
clientCredentialsIdx: Integer;
req: TChilkatHttpRequest;
accessToken: WideString;

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

http := TChilkatHttp.Create(Self);

// The first step is to fetch your IdentityServer4's discovery document
// (OpenID Connect defines a discovery mechanism, called OpenID Connect Discovery, where an OpenID server publishes its metadata at a well-known URL, 
// typically https://server.com/.well-known/openid-configuration

resp := http.QuickRequest('GET','https://localhost:5000/.well-known/openid-configuration');
if (http.LastMethodSuccess <> 1) then
  begin
    Memo1.Lines.Add(http.LastErrorText);
    Exit;
  end;

if (resp.StatusCode <> 200) then
  begin
    Memo1.Lines.Add('Received response status code ' + IntToStr(resp.StatusCode));
    Memo1.Lines.Add('Response body containing error text or JSON:');
    Memo1.Lines.Add(resp.BodyStr);

    Exit;
  end;

json := TChilkatJsonObject.Create(Self);
success := json.Load(resp.BodyStr);

// We have the discovery document, which contains something like this:

// You can use this online tool to generate parsing code from sample JSON: 
// Generate Parsing Code from JSON

// {
//   "issuer": "https://localhost:5000",
//   "jwks_uri": "https://localhost:5000/.well-known/openid-configuration/jwks",
//   "authorization_endpoint": "https://localhost:5000/connect/authorize",
//   "token_endpoint": "https://localhost:5000/connect/token",
//   "userinfo_endpoint": "https://localhost:5000/connect/userinfo",
//   "end_session_endpoint": "https://localhost:5000/connect/endsession",
//   "check_session_iframe": "https://localhost:5000/connect/checksession",
//   "revocation_endpoint": "https://localhost:5000/connect/revocation",
//   "introspection_endpoint": "https://localhost:5000/connect/introspect",
//   "frontchannel_logout_supported": true,
//   "frontchannel_logout_session_supported": true,
//   "backchannel_logout_supported": true,
//   "backchannel_logout_session_supported": true,
//   "scopes_supported": [
//     "openid",
//     "profile",
//     "email",
//     "MyCompany.profile",
//     "MyCompany.Identity.WebApi",
//     "MyCompany.TriHub.WebApi",
//     "offline_access"
//   ],
//   "claims_supported": [
//     "sub",
//     "updated_at",
//     "locale",
//     "zoneinfo",
//     "birthdate",
//     "gender",
//     "website",
//     "profile",
//     "preferred_username",
//     "nickname",
//     "middle_name",
//     "given_name",
//     "family_name",
//     "name",
//     "picture",
//     "email_verified",
//     "email",
//     "userId",
//     "groups",
//     "fullname"
//   ],
//   "grant_types_supported": [
//     "authorization_code",
//     "client_credentials",
//     "refresh_token",
//     "implicit",
//     "password"
//   ],
//   "response_types_supported": [
//     "code",
//     "token",
//     "id_token",
//     "id_token token",
//     "code id_token",
//     "code token",
//     "code id_token token"
//   ],
//   "response_modes_supported": [
//     "form_post",
//     "query",
//     "fragment"
//   ],
//   "token_endpoint_auth_methods_supported": [
//     "client_secret_basic",
//     "client_secret_post"
//   ],
//   "subject_types_supported": [
//     "public"
//   ],
//   "id_token_signing_alg_values_supported": [
//     "RS256"
//   ],
//   "code_challenge_methods_supported": [
//     "plain",
//     "S256"
//   ]
// }
// 

// The next steps are to (1) get the token_endpoint,
// and (2) verify that the client_credentials grant type is supported.

tokenEndpoint := json.StringOf('token_endpoint');

grantTypes := json.ArrayOf('grant_types_supported');
clientCredentialsIdx := grantTypes.FindString('client_credentials',1);

// If clientCredentialsIdx is less then zero (-1) then the "client_credentials" string was not found.
if (clientCredentialsIdx < 0) then
  begin
    Memo1.Lines.Add('The client credentials grant type is not supported.');
    Exit;
  end;

// Request the access token using our Client ID and Client Secret.
// We're going to duplicate this CURL statement:

// curl --request POST \
//   --url '<tokenEndpoint>' \
//   --header 'content-type: application/x-www-form-urlencoded' \
//   --data 'grant_type=client_credentials&client_id=CLIENT_ID&client_secret=CLIENT_SECRET'

req := TChilkatHttpRequest.Create(Self);
req.HttpVerb := 'POST';
req.AddParam('grant_type','client_credentials');
req.AddParam('client_id','CLIENT_ID');
req.AddParam('client_secret','CLIENT_SECRET');

resp := http.PostUrlEncoded(tokenEndpoint,req.ControlInterface);
if (http.LastMethodSuccess = 0) then
  begin
    Memo1.Lines.Add(http.LastErrorText);
    Exit;
  end;

// Make sure we got a 200 response status code, otherwise it's an error.
if (resp.StatusCode <> 200) then
  begin
    Memo1.Lines.Add('POST to token endpoint failed.');
    Memo1.Lines.Add('Received response status code ' + IntToStr(resp.StatusCode));
    Memo1.Lines.Add('Response body containing error text or JSON:');
    Memo1.Lines.Add(resp.BodyStr);

    Exit;
  end;

success := json.Load(resp.BodyStr);

// Our JSON response should contain this:
// {
//   "access_token":"eyJz93a...k4laUWw",
//   "token_type":"Bearer",
//   "expires_in":86400
// }

// Get the access token:
accessToken := json.StringOf('access_token');

// The access token is what gets added to "Authorization: Bearer <access_token>"
// for the subsequent REST API calls..
end;