63 lines
2.3 KiB
Go
63 lines
2.3 KiB
Go
// Package admin is the gateway's admin edge: HTTP Basic-Auth in front of a reverse
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// proxy that forwards the operator's browser to the backend's server-rendered admin
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// console under /_gm. The proxy is mounted at /_gm/ on the gateway's public listener
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// (below the h2c wrap, see internal/connectsrv) and forwards verbatim — an inbound
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// /_gm/<rest> reaches <backendURL>/_gm/<rest>, preserving the inbound Host so the
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// backend's same-origin check sees the public origin. The backend trusts the gateway
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// on this segment and adds the console's same-origin CSRF guard
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// (docs/ARCHITECTURE.md §12).
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package admin
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import (
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"crypto/subtle"
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"fmt"
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"net/http"
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"net/http/httputil"
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"net/url"
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"go.uber.org/zap"
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)
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// NewProxy returns a handler that checks Basic-Auth against user/password and
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// reverse-proxies the request verbatim to the backend: the inbound path is
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// preserved, so /_gm/<rest> reaches <backendURL>/_gm/<rest>. It is mounted at /_gm/
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// on the gateway's public listener.
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func NewProxy(backendURL, user, password string, log *zap.Logger) (http.Handler, error) {
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target, err := url.Parse(backendURL)
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if err != nil {
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return nil, fmt.Errorf("admin: parse backend url %q: %w", backendURL, err)
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}
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if log == nil {
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log = zap.NewNop()
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}
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proxy := &httputil.ReverseProxy{
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Rewrite: func(pr *httputil.ProxyRequest) {
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pr.SetURL(target) // backend scheme+host; the inbound /_gm path is preserved
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pr.Out.Host = pr.In.Host // keep the public Host for the backend same-origin check
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},
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ErrorHandler: func(w http.ResponseWriter, r *http.Request, err error) {
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log.Warn("admin proxy upstream error", zap.String("path", r.URL.Path), zap.Error(err))
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w.WriteHeader(http.StatusBadGateway)
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},
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}
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return basicAuth(user, password, proxy), nil
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}
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// basicAuth wraps next with a constant-time Basic-Auth check.
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func basicAuth(user, password string, next http.Handler) http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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u, p, ok := r.BasicAuth()
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if !ok || !equal(u, user) || !equal(p, password) {
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w.Header().Set("WWW-Authenticate", `Basic realm="scrabble-admin"`)
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http.Error(w, "unauthorized", http.StatusUnauthorized)
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return
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}
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next.ServeHTTP(w, r)
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})
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}
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// equal compares two strings in constant time.
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func equal(a, b string) bool {
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return subtle.ConstantTimeCompare([]byte(a), []byte(b)) == 1
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}
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