authenticate: refactor middleware, logging, and tests (#30)

- Abstract remaining middleware from authenticate into internal.
- Use middleware chaining in authenticate.
- Standardize naming of Request and ResponseWriter to match std lib.
- Add healthcheck / ping as a middleware.
- Internalized wraped_writer package adapted from goji/middleware.
- Fixed indirection issue with reverse proxy map.

internal/log/log.go

@@ -3,6 +3,7 @@ package log // import "github.com/pomerium/pomerium/internal/log"
 
 import (
 	"context"
+	"net/http"
 	"os"
 
 	"github.com/rs/zerolog"
@@ -102,3 +103,9 @@ func Printf(format string, v ...interface{}) {
 func Ctx(ctx context.Context) *zerolog.Logger {
 	return zerolog.Ctx(ctx)
 }
+
+// FromRequest gets the logger in the request's context.
+// This is a shortcut for log.Ctx(r.Context())
+func FromRequest(r *http.Request) *zerolog.Logger {
+	return Ctx(r.Context())
+}