Added Const for use of CtxKeys (#1511)

* Added Const for CtxKeys

* Move CtxKey Const declarations

* Fixed tests

* fix test

caddyhttp/httpserver/mitm.go

@@ -9,8 +9,6 @@ import (
 	"net/http"
 	"strings"
 	"sync"
-
-	"github.com/mholt/caddy"
 )
 
 // tlsHandler is a http.Handler that will inject a value
@@ -74,7 +72,7 @@ func (h *tlsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if checked {
-		r = r.WithContext(context.WithValue(r.Context(), caddy.CtxKey("mitm"), mitm))
+		r = r.WithContext(context.WithValue(r.Context(), MitmCtxKey, mitm))
 	}
 
 	if mitm && h.closeOnMITM {