Openid tokenintrospection request uses the wrong form key

[herojan]

Expected:
The filter oauthTokenintrospectionAllKV("http://configurl", "key", "value") should call the introspection_endpoint with form parameters token=$token as per https://tools.ietf.org/html/rfc7662#section-2.1

Actual:
The filter sends the form parameters access_token=$token

See:

skipper/filters/auth/authclient.go

Line 105 in 3a77112

body.Add(accessTokenKey, auth)

I can create a PR to change this if it's wanted?

[szuecs]

Yes please, weird I thought I checked it against one of our IAM backends.
Can you create a PR to change https://github.com/zalando/skipper/blob/master/filters/auth/auth.go#L48 variable and check where it it used?
It should be only used in the oauthTokenintrospection* filters and if so it's fine to fix it according to the RFC.

[herojan]

Grand, I opened a pr for it #811