var
  APIURL: string = 'https://localhost:8080/';
//…

constructor TServerRequest.Create(const AServerURL: string);
var
  Http: TIdCustomHTTP;
  SSLIOHandler: TIdSSLIOHandlerSocketOpenSSL;
begin
  FServerURL := AServerURL;
  //...
  FRESTClient := TRESTClient.Create(nil);
  FRESTRequest := TRESTRequest.Create(nil);
  FRESTRequest.Client := FRESTClient;

  //... добавлено нижеследующее 
  IdOpenSSLSetLibPath('E:\SSL\'); // path exists
  Http := (FRESTRequest.Client.HTTPClient.Peer.GetObject) as TIdCustomHTTP;
  SSLIOHandler := TIdSSLIOHandlerSocketOpenSSL.Create(Http);
  with SSLIOHandler do
  begin
    SSLOptions.Method := sslvSSLv3;
    SSLOptions.SSLVersions := [sslvSSLv3];
  end;
  Http.IOHandler := SSLIOHandler;
  //...

end;

///….. в методе TServerRequest вызываю
    FRESTClient.BaseURL := FServerURL + 'auth/openid-connect/token';
    FRESTRequest.AddAuthParameter('Authorization', 'Bearer ' + TResourceBearer(Resource).Token, pkHTTPHEADER, [poDoNotEncode]);
///….. 
    FRESTRequest.Method := rmPOST;
    FRESTRequest.Execute;