OIDC: Fix issues with subset of services.

[eloycoto]

By default, APICast stores all services in an array of Service Objects, also,
another array with the OIDC objects, something like this:

{
  "services": [
    {
      "id": 1,
      "issuer": "http://foo.com",
      "auth_type": "oidc",
      ...
    },
    {
      "id": 2,
      "auth_type": "provider_key"
      ...
    },
    {
      "id": 3,
      "issuer": "http://bar.com",
      "auth_type": "oidc",
      ...
    }
  ],
  "oidc": [
    {
      "issuer": "http://foo.com",
      ...
    },
    false,
    {
      "issuer": "http://bar.com",
      ...
    }
  ]
}

The mapping, on APICast config is like this:

service[0] using oidc[0]
service[1] using oidc[1]
service[2] using oidc[2]

When we filter using APICAST_SERVICE_LIST, it filters based on the array, so
it'll transform to this:

export APICAST_SERVICE_LIST=3

{
  "services": [
    {
      "id": 3,
      "issuer": "http://bar.com",
      "auth_type": "oidc",
      ...
    }
  ],
  "oidc": [
    false,
    {
      "issuer": "http://bar.com",
      ...
    }
  ]
}

So, OIDC will fail, because the first entry of the OIDC array is false, because
false is added on filtering.

This PR added a new entry on oidc object, that it's service_id, so filtering can
be done without issues, config will be like this:

{
  "services": [
    {
      "id": 1,
      "issuer": "http://foo.com",
      "auth_type": "oidc",
      ...
    },
    {
      "id": 2,
      "auth_type": "provider_key"
      ...
    },
    {
      "id": 3,
      "issuer": "http://bar.com",
      "auth_type": "oidc",
      ...
    }
  ],
  "oidc": [
    {
      "issuer": "http://foo.com",
      "service_id": 1,
      ...
    },
    {
      "service_id": 2,
    },
    {
      "issuer": "http://bar.com",
      "service_id": 3,
      ...
    }
  ]
}

On non-oidc services, the oidc will be not hitted at all. On invalid fetch,
It'll be not fail, because the issuer is not in there, so it'll not work as
expected.

OIDC config links:

Service OIDC setup:

APIcast/gateway/src/apicast/configuration/service.lua

Lines 221 to 231 in c184ff3

	function _M:oauth()
	local authentication = self.authentication_method or self.backend_version
	if authentication == 'oidc' then
	return oauth.oidc.new(self.oidc)
	elseif authentication == 'oauth' then
	return oauth.apicast.new(self)
	else
	return nil, 'not oauth'
	end
	end

OIDC error on invalid oicd setup:

APIcast/gateway/src/apicast/oauth/oidc.lua

Line 55 in c184ff3

err = 'missing OIDC configuration'

Warning message:

APIcast/gateway/src/apicast/proxy.lua

Lines 199 to 205 in c184ff3

	if oauth then
	ngx.log(ngx.DEBUG, 'using OAuth: ', oauth)
	if err then
	ngx.log(ngx.WARN, 'failed to initialize ', oauth, ' for service ', service.id, ': ', err)
	end
	end

Filtering part:
https://github.com/3scale/APIcast/blob/c184ff3e904f3d75857032a3da0004f8d74eba00/gateway/src/apicast/configuration.lua#L173-L297

Fix: THREESCALE-6042
Reported-by: Kevin Price kevprice@redhat.com
Reported-by: Samuele Illuminati sillumin@redhat.com
Signed-off-by: Eloy Coto eloy.coto@acalustra.com

[unleashed]

LGTM