code: def build_signature(self, user_api_key, user_secret, request):
          
          path = request.get_full_path()
          sent_signature = request.META.get(
              self.header_canonical('Authorization'))
          signature_headers = self.get_headers_from_signature(sent_signature)
          unsigned = self.build_dict_to_sign(request, signature_headers)
  
          # Sign string and compare.
          signer = HeaderSigner(
              key_id=user_api_key, secret=user_secret,
              headers=signature_headers, algorithm=self.ALGORITHM)
          signed = signer.sign(unsigned, method=request.method, path=path)
          return signed['authorization']
docs: Return the signature for the request.