ios – Easy methods to create secIdentity with certificates from trusted server

How can I create secIdentity from utilizing the DigiCert World Root G2 from https://study.microsoft.com/en-us/azure/safety/fundamentals/azure-ca-details?tabs=root-and-subordinate-cas-list
Because it is not going to have key.
I would like to make use of in mqtt SSL authentication as talked about https://github.com/emqx/CocoaMQTT/blob/4abf2d10315dff60661a32f1db5dcc45a9df9f09/Instance/Instance/ViewController.swift#L183 but it surely have .p12 with password

I used to be making an attempt one thing like this however its not working.

      func loadCACertificate() -> CFArray?{
          let certFilePath = Bundle.principal.path(forResource: "DigiCertGlobalRootG2", ofType: "crt")! 

          let certData = strive! Information(contentsOf: URL(fileURLWithPath: certFilePath))
          let certDataNS =  NSData(contentsOf: URL(fileURLWithPath: certFilePath))
          print("Certificates knowledge: (String(describing: certDataNS))")
          let rootCertificate = (SecCertificateCreateWithData(nil, certData as CFData) ?? "" as! SecCertificate) as SecCertificate
                  print("Root certificates: (rootCertificate)")
          
          return rootCertificate
      }