*: add an OpenID Connect provider

See the README for usage with Dex or any other OIDC provider.

To test run a backend:

    python3 -m http.server

Run dex and modify the example config with the proxy callback:

    go get github.com/coreos/dex/cmd/dex
    cd $GOPATH/src/github.com/coreos/dex
    sed -i.bak \
      's|http://127.0.0.1:5555/callback|http://127.0.0.1:5555/oauth2/callback|g' \
       examples/config-dev.yaml
    make
    ./bin/dex serve examples/config-dev.yaml

Then run the oauth2_proxy

    oauth2_proxy \
      --oidc-issuer-url http://127.0.0.1:5556/dex \
      --upstream http://localhost:8000 \
      --client-id example-app \
      --client-secret ZXhhbXBsZS1hcHAtc2VjcmV0 \
      --cookie-secret foo \
      --email-domain '*' \
      --http-address http://127.0.0.1:5555 \
      --redirect-url http://127.0.0.1:5555/oauth2/callback \
      --cookie-secure=false

Login with the username/password "admin@example.com:password"

Godeps

@@ -8,3 +8,6 @@ golang.org/x/oauth2                      7fdf09982454086d5570c7db3e11f360194830c
 golang.org/x/net/context                 242b6b35177ec3909636b6cf6a47e8c2c6324b5d
 google.golang.org/api/admin/directory/v1 650535c7d6201e8304c92f38c922a9a3a36c6877
 cloud.google.com/go/compute/metadata     v0.7.0
+github.com/coreos/go-oidc                c797a55f1c1001ec3169f1d0fbb4c5523563bec6
+gopkg.in/square/go-jose.v2               v2.1.1
+github.com/pquerna/cachecontrol          9299cc36e57c32f83e47ffb3c25d8a3dec10ea0b