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basicauth.go
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basicauth.go
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// Package basicauth implements HTTP Basic Authentication for Caddy.
//
// This is useful for simple protections on a website, like requiring
// a password to access an admin interface. This package assumes a
// fairly small threat model.
package basicauth
import (
"bufio"
"context"
"crypto/sha1"
"crypto/subtle"
"fmt"
"io"
"net/http"
"os"
"path/filepath"
"strings"
"sync"
"github.com/jimstudt/http-authentication/basic"
"github.com/mholt/caddy/caddyhttp/httpserver"
)
// BasicAuth is middleware to protect resources with a username and password.
// Note that HTTP Basic Authentication is not secure by itself and should
// not be used to protect important assets without HTTPS. Even then, the
// security of HTTP Basic Auth is disputed. Use discretion when deciding
// what to protect with BasicAuth.
type BasicAuth struct {
Next httpserver.Handler
SiteRoot string
Rules []Rule
}
// ServeHTTP implements the httpserver.Handler interface.
func (a BasicAuth) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
var protected, isAuthenticated bool
var realm string
for _, rule := range a.Rules {
for _, res := range rule.Resources {
if !httpserver.Path(r.URL.Path).Matches(res) {
continue
}
// path matches; this endpoint is protected
protected = true
realm = rule.Realm
// parse auth header
username, password, ok := r.BasicAuth()
// check credentials
if !ok ||
username != rule.Username ||
!rule.Password(password) {
continue
}
// by this point, authentication was successful
isAuthenticated = true
// let upstream middleware (e.g. fastcgi and cgi) know about authenticated
// user; this replaces the request with a wrapped instance
r = r.WithContext(context.WithValue(r.Context(),
httpserver.RemoteUserCtxKey, username))
}
}
if protected && !isAuthenticated {
// browsers show a message that says something like:
// "The website says: <realm>"
// which is kinda dumb, but whatever.
if realm == "" {
realm = "Restricted"
}
w.Header().Set("WWW-Authenticate", "Basic realm=\""+realm+"\"")
return http.StatusUnauthorized, nil
}
// Pass-through when no paths match
return a.Next.ServeHTTP(w, r)
}
// Rule represents a BasicAuth rule. A username and password
// combination protect the associated resources, which are
// file or directory paths.
type Rule struct {
Username string
Password func(string) bool
Resources []string
Realm string // See RFC 1945 and RFC 2617, default: "Restricted"
}
// PasswordMatcher determines whether a password matches a rule.
type PasswordMatcher func(pw string) bool
var (
htpasswords map[string]map[string]PasswordMatcher
htpasswordsMu sync.Mutex
)
// GetHtpasswdMatcher matches password rules.
func GetHtpasswdMatcher(filename, username, siteRoot string) (PasswordMatcher, error) {
filename = filepath.Join(siteRoot, filename)
htpasswordsMu.Lock()
if htpasswords == nil {
htpasswords = make(map[string]map[string]PasswordMatcher)
}
pm := htpasswords[filename]
if pm == nil {
fh, err := os.Open(filename)
if err != nil {
return nil, fmt.Errorf("open %q: %v", filename, err)
}
defer fh.Close()
pm = make(map[string]PasswordMatcher)
if err = parseHtpasswd(pm, fh); err != nil {
return nil, fmt.Errorf("parsing htpasswd %q: %v", fh.Name(), err)
}
htpasswords[filename] = pm
}
htpasswordsMu.Unlock()
if pm[username] == nil {
return nil, fmt.Errorf("username %q not found in %q", username, filename)
}
return pm[username], nil
}
func parseHtpasswd(pm map[string]PasswordMatcher, r io.Reader) error {
scanner := bufio.NewScanner(r)
for scanner.Scan() {
line := strings.TrimSpace(scanner.Text())
if line == "" || strings.IndexByte(line, '#') == 0 {
continue
}
i := strings.IndexByte(line, ':')
if i <= 0 {
return fmt.Errorf("malformed line, no color: %q", line)
}
user, encoded := line[:i], line[i+1:]
for _, p := range basic.DefaultSystems {
matcher, err := p(encoded)
if err != nil {
return err
}
if matcher != nil {
pm[user] = matcher.MatchesPassword
break
}
}
}
return scanner.Err()
}
// PlainMatcher returns a PasswordMatcher that does a constant-time
// byte comparison against the password passw.
func PlainMatcher(passw string) PasswordMatcher {
// compare hashes of equal length instead of actual password
// to avoid leaking password length
passwHash := sha1.New()
passwHash.Write([]byte(passw))
passwSum := passwHash.Sum(nil)
return func(pw string) bool {
pwHash := sha1.New()
pwHash.Write([]byte(pw))
pwSum := pwHash.Sum(nil)
return subtle.ConstantTimeCompare([]byte(pwSum), []byte(passwSum)) == 1
}
}