code: def _custom_validate(self, verify, trust_bundle):
          
          # If we disabled cert validation, just say: cool.
          if not verify:
              return
  
          # We want data in memory, so load it up.
          if os.path.isfile(trust_bundle):
              with open(trust_bundle, 'rb') as f:
                  trust_bundle = f.read()
  
          cert_array = None
          trust = Security.SecTrustRef()
  
          try:
              # Get a CFArray that contains the certs we want.
              cert_array = _cert_array_from_pem(trust_bundle)
  
              # Ok, now the hard part. We want to get the SecTrustRef that ST has
              # created for this connection, shove our CAs into it, tell ST to
              # ignore everything else it knows, and then ask if it can build a
              # chain. This is a buuuunch of code.
              result = Security.SSLCopyPeerTrust(
                  self.context, ctypes.byref(trust)
              )
              _assert_no_error(result)
              if not trust:
                  raise ssl.SSLError("Failed to copy trust reference")
  
              result = Security.SecTrustSetAnchorCertificates(trust, cert_array)
              _assert_no_error(result)
  
              result = Security.SecTrustSetAnchorCertificatesOnly(trust, True)
              _assert_no_error(result)
  
              trust_result = Security.SecTrustResultType()
              result = Security.SecTrustEvaluate(
                  trust, ctypes.byref(trust_result)
              )
              _assert_no_error(result)
          finally:
              if trust:
                  CoreFoundation.CFRelease(trust)
  
              if cert_array is not None:
                  CoreFoundation.CFRelease(cert_array)
  
          # Ok, now we can look at what the result was.
          successes = (
              SecurityConst.kSecTrustResultUnspecified,
              SecurityConst.kSecTrustResultProceed
          )
          if trust_result.value not in successes:
              raise ssl.SSLError(
                  "certificate verify failed, error code: %d" %
                  trust_result.value
              )
docs: Called when we have set custom validation. We do this in two cases:
          first, when cert validation is entirely disabled; and second, when
          using a custom trust DB.