Simple SAML2 SP in pure Python for Google App Engine Standard Environment

We need a simple implementation for a SAML 2.0 Service Provider (SP) in pure Python, using only the libraries available at Google App Engine Standard Environment (e.g. pycrypto) with webapp2. In order to keep it simple, the IdP and SP metadata should be hardcoded, as well as the SP public and private keys in PEM format (so there is no need to use the file system). The aim is basically to: (1) create the AuthNRequest XML and sign it, (2) redirect to the IP endpoint, (3) process the IP XML posted message and (4) verify that it is correctly signed.