docs: def _sha256_sign(self, method, url, headers, body):
          """Sign the request with SHA256.
          """
          d = ''
          sign_headers = method.upper() + '|' + url + '|'
          for key, value in sorted(headers.items()):
              if key.startswith('X-Mcash-'):
                  sign_headers += d + key.upper() + '=' + value
                  d = '&'
  
          rsa_signature = base64.b64encode(
              self.signer.sign(SHA256.new(sign_headers)))
  
          return 'RSA-SHA256 ' + rsa_signature