request help: Support forward-auth

[GhangZh]

Issue description

We are using traefik and want to migrate to apisix, but traefik has a forward-auth plugin, which is a plugin that supports external authentication services, how does apisix support external authentication services?

Environment

• apisix version (cmd: apisix version):2.10.0
• OS (cmd: uname -a):
• OpenResty / Nginx version (cmd: nginx -V or openresty -V):openresty/1.19.3.1
• etcd version, if have (cmd: run curl http://127.0.0.1:9090/v1/server_info to get the info from server-info API):
• apisix-dashboard version, if have:
• the plugin runner version, if the issue is about a plugin runner (cmd: depended on the kind of runner):
• luarocks version, if the issue is about installation (cmd: luarocks --version):

[spacewander]

Can you provide more details about the forward-auth plugin and how do you use it?

[tzssangglass]

This auth model looks like openid-connect or ladp-auth,

openid-connect: https://github.com/apache/apisix/blob/master/docs/en/latest/plugins/openid-connect.md

ladp-auth: https://github.com/apache/apisix/blob/master/docs/en/latest/plugins/ldap-auth.md

[GhangZh]

I just want to use our own authentication service. In apisix, I want to set the domain name of the service through the annotation: "ingress.kubernetes.io/auth-url":http://xxxxxx, and hand it over to this service to get the authentication result. If the verification is passed, continue, if not Pass , stop.