Possibility to test SAML2 and OIDC Proxy

[peppelinux]

an additional option, like --proxy saml2|oidc|oauth2 would load a specialized authnrequest loader, for each kind of proxy type.
This will follow the requests if they are saml2 redirect or post or oidc/oauth2 auth code flow.

This is a approach that would be experimental, each tested proxy as working would be referenced in a dedicated section in the README.

the proxy that would drive the first tests are:

SATOSA-Saml2SPID
AgID Login (oidc auth code flow)

[peppelinux]

This feature Is implemented with the help of authn plugins
af22d98

We needs to get some contribution and examples. The First proxy plugin Will cover satosa-saml2spid and It would a good starting point, as well, for others

[peppelinux]

Satosa-Saml2Spid IAM Proxy covered here

spid-sp-test/src/spid_sp_test/plugins/authn_request.py

Line 39 in 12d72a9

class SatosaSaml2Spid(Base):

it could be a good starting point for every Saml2Saml proxies

[peppelinux]

linked to this
#65