use package level defined contextKey as context key

rest/internal/context/params.go

@@ -5,7 +5,7 @@ import (
 	"net/http"
 )
 
-const pathVars = "pathVars"
+var pathVars = contextKey("pathVars")
 
 func Vars(r *http.Request) map[string]string {
 	vars, ok := r.Context().Value(pathVars).(map[string]string)
@@ -19,3 +19,9 @@ func Vars(r *http.Request) map[string]string {
 func WithPathVars(r *http.Request, params map[string]string) *http.Request {
 	return r.WithContext(context.WithValue(r.Context(), pathVars, params))
 }
+
+type contextKey string
+
+func (c contextKey) String() string {
+	return "rest/internal/context context key" + string(c)
+}