AuthnResponse fails to extract name_id (NAME_ID_FORMAT)

I'm using latest version 3.12, and Google as both identity and service provider and i'm getting SamlAuthError("No name_id in SAML response.") at django_saml2_auth/saml.py line 315.
I've been debugging for quite some time but I'm unable to figure out what is causing the problem, or find any solution online.

This is my config:

SAML2_AUTH = {
    ...
    "NAME_ID_FORMAT": "<urn:oasis:names:tc:SAML:2.0:nameid-format:transient>"
}

GoogleIDPMetadata.xml:

<md:EntityDescriptor>
  <md:IDPSSODescriptor>
  ...
    <md:NameIDFormat>urn:oasis:names:tc:SAML:2.0:nameid-format:transient</md:NameIDFormat>
    <md:SingleSignOnService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Redirect" Location="https://accounts.google.com/o/saml2/idp?idpid=<ID>"/>
    <md:SingleSignOnService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" Location="https://accounts.google.com/o/saml2/idp?idpid=<ID>"/>
  </md:IDPSSODescriptor>
</md:EntityDescriptor>

Auth response received:

<saml2p:Response xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol" Destination="..." ID="..." IssueInstant="..." Version="2.0">
    <saml2p:Status>
        <saml2p:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
    </saml2p:Status>
    <saml2:Assertion xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion" ID="..." IssueInstant="..." Version="2.0">
        <saml2:Subject>
            <saml2:NameID Format="urn:oasis:names:tc:SAML:2.0:nameid-format:transient">test-email@domain.com</saml2:NameID>
            ...
        </saml2:Subject>
        ...
    </saml2:Assertion>
</saml2p:Response>

Seems like NameID Format is consistent and valid but regardless it's always None. Only place a was able to find value being set is in response.py at line 765 in get_subject method, called from _assertion method, but those methods are not called before saml response is decoded:

        # The subject may contain a name_id

        if subject.name_id:
            self.name_id = subject.name_id

There is a related pr #264 but solution doesn't work for me. Result is the same regardless of what I set as NAME_ID_FORMAT so I'm suspecting problem lies somewhere else.

Any help would be much appreciated

grafana / django-saml2-auth

AuthnResponse fails to extract name_id (NAME_ID_FORMAT) #315