mirror of
https://github.com/caddyserver/caddy.git
synced 2025-11-03 11:07:23 -05:00
303 lines
9.5 KiB
Go
303 lines
9.5 KiB
Go
// Copyright 2015 Matthew Holt and The Caddy Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package caddyauth
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import (
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"encoding/base64"
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"encoding/hex"
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"encoding/json"
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"fmt"
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weakrand "math/rand"
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"net/http"
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"strings"
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"sync"
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"golang.org/x/sync/singleflight"
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"github.com/caddyserver/caddy/v2"
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)
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func init() {
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caddy.RegisterModule(HTTPBasicAuth{})
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}
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// HTTPBasicAuth facilitates HTTP basic authentication.
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type HTTPBasicAuth struct {
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// The algorithm with which the passwords are hashed. Default: bcrypt
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HashRaw json.RawMessage `json:"hash,omitempty" caddy:"namespace=http.authentication.hashes inline_key=algorithm"`
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// The list of accounts to authenticate.
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AccountList []Account `json:"accounts,omitempty"`
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// The name of the realm. Default: restricted
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Realm string `json:"realm,omitempty"`
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// If non-nil, a mapping of plaintext passwords to their
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// hashes will be cached in memory (with random eviction).
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// This can greatly improve the performance of traffic-heavy
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// servers that use secure password hashing algorithms, with
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// the downside that plaintext passwords will be stored in
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// memory for a longer time (this should not be a problem
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// as long as your machine is not compromised, at which point
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// all bets are off, since basicauth necessitates plaintext
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// passwords being received over the wire anyway). Note that
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// a cache hit does not mean it is a valid password.
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HashCache *Cache `json:"hash_cache,omitempty"`
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Accounts map[string]Account `json:"-"`
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Hash Comparer `json:"-"`
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// fakePassword is used when a given user is not found,
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// so that timing side-channels can be mitigated: it gives
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// us something to hash and compare even if the user does
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// not exist, which should have similar timing as a user
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// account that does exist.
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fakePassword []byte
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}
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// CaddyModule returns the Caddy module information.
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func (HTTPBasicAuth) CaddyModule() caddy.ModuleInfo {
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return caddy.ModuleInfo{
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ID: "http.authentication.providers.http_basic",
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New: func() caddy.Module { return new(HTTPBasicAuth) },
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}
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}
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// Provision provisions the HTTP basic auth provider.
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func (hba *HTTPBasicAuth) Provision(ctx caddy.Context) error {
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if hba.HashRaw == nil {
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hba.HashRaw = json.RawMessage(`{"algorithm": "bcrypt"}`)
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}
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// load password hasher
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hasherIface, err := ctx.LoadModule(hba, "HashRaw")
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if err != nil {
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return fmt.Errorf("loading password hasher module: %v", err)
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}
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hba.Hash = hasherIface.(Comparer)
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if hba.Hash == nil {
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return fmt.Errorf("hash is required")
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}
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// if supported, generate a fake password we can compare against if needed
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if hasher, ok := hba.Hash.(Hasher); ok {
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hba.fakePassword = hasher.FakeHash()
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}
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repl := caddy.NewReplacer()
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// load account list
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hba.Accounts = make(map[string]Account)
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for i, acct := range hba.AccountList {
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if _, ok := hba.Accounts[acct.Username]; ok {
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return fmt.Errorf("account %d: username is not unique: %s", i, acct.Username)
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}
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acct.Username = repl.ReplaceAll(acct.Username, "")
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acct.Password = repl.ReplaceAll(acct.Password, "")
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if acct.Username == "" || acct.Password == "" {
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return fmt.Errorf("account %d: username and password are required", i)
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}
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// TODO: Remove support for redundantly-encoded b64-encoded hashes
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// Passwords starting with '$' are likely in Modular Crypt Format,
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// so we don't need to base64 decode them. But historically, we
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// required redundant base64, so we try to decode it otherwise.
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if strings.HasPrefix(acct.Password, "$") {
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acct.password = []byte(acct.Password)
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} else {
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acct.password, err = base64.StdEncoding.DecodeString(acct.Password)
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if err != nil {
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return fmt.Errorf("base64-decoding password: %v", err)
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}
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}
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hba.Accounts[acct.Username] = acct
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}
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hba.AccountList = nil // allow GC to deallocate
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if hba.HashCache != nil {
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hba.HashCache.cache = make(map[string]bool)
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hba.HashCache.mu = new(sync.RWMutex)
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hba.HashCache.g = new(singleflight.Group)
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}
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return nil
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}
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// Authenticate validates the user credentials in req and returns the user, if valid.
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func (hba HTTPBasicAuth) Authenticate(w http.ResponseWriter, req *http.Request) (User, bool, error) {
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username, plaintextPasswordStr, ok := req.BasicAuth()
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if !ok {
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return hba.promptForCredentials(w, nil)
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}
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account, accountExists := hba.Accounts[username]
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if !accountExists {
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// don't return early if account does not exist; we want
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// to try to avoid side-channels that leak existence, so
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// we use a fake password to simulate realistic CPU cycles
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account.password = hba.fakePassword
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}
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same, err := hba.correctPassword(account, []byte(plaintextPasswordStr))
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if err != nil || !same || !accountExists {
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return hba.promptForCredentials(w, err)
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}
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return User{ID: username}, true, nil
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}
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func (hba HTTPBasicAuth) correctPassword(account Account, plaintextPassword []byte) (bool, error) {
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compare := func() (bool, error) {
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return hba.Hash.Compare(account.password, plaintextPassword)
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}
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// if no caching is enabled, simply return the result of hashing + comparing
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if hba.HashCache == nil {
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return compare()
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}
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// compute a cache key that is unique for these input parameters
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cacheKey := hex.EncodeToString(append(account.password, plaintextPassword...))
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// fast track: if the result of the input is already cached, use it
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hba.HashCache.mu.RLock()
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same, ok := hba.HashCache.cache[cacheKey]
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hba.HashCache.mu.RUnlock()
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if ok {
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return same, nil
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}
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// slow track: do the expensive op, then add it to the cache
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// but perform it in a singleflight group so that multiple
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// parallel requests using the same password don't cause a
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// thundering herd problem by all performing the same hashing
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// operation before the first one finishes and caches it.
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v, err, _ := hba.HashCache.g.Do(cacheKey, func() (any, error) {
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return compare()
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})
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if err != nil {
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return false, err
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}
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same = v.(bool)
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hba.HashCache.mu.Lock()
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if len(hba.HashCache.cache) >= 1000 {
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hba.HashCache.makeRoom() // keep cache size under control
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}
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hba.HashCache.cache[cacheKey] = same
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hba.HashCache.mu.Unlock()
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return same, nil
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}
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func (hba HTTPBasicAuth) promptForCredentials(w http.ResponseWriter, err error) (User, bool, error) {
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// browsers show a message that says something like:
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// "The website says: <realm>"
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// which is kinda dumb, but whatever.
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realm := hba.Realm
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if realm == "" {
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realm = "restricted"
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}
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w.Header().Set("WWW-Authenticate", fmt.Sprintf(`Basic realm="%s"`, realm))
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return User{}, false, err
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}
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// Cache enables caching of basic auth results. This is especially
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// helpful for secure password hashes which can be expensive to
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// compute on every HTTP request.
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type Cache struct {
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mu *sync.RWMutex
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g *singleflight.Group
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// map of concatenated hashed password + plaintext password, to result
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cache map[string]bool
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}
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// makeRoom deletes about 1/10 of the items in the cache
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// in order to keep its size under control. It must not be
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// called without a lock on c.mu.
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func (c *Cache) makeRoom() {
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// we delete more than just 1 entry so that we don't have
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// to do this on every request; assuming the capacity of
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// the cache is on a long tail, we can save a lot of CPU
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// time by doing a whole bunch of deletions now and then
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// we won't have to do them again for a while
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numToDelete := len(c.cache) / 10
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if numToDelete < 1 {
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numToDelete = 1
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}
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for deleted := 0; deleted <= numToDelete; deleted++ {
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// Go maps are "nondeterministic" not actually random,
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// so although we could just chop off the "front" of the
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// map with less code, this is a heavily skewed eviction
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// strategy; generating random numbers is cheap and
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// ensures a much better distribution.
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//nolint:gosec
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rnd := weakrand.Intn(len(c.cache))
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i := 0
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for key := range c.cache {
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if i == rnd {
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delete(c.cache, key)
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break
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}
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i++
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}
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}
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}
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// Comparer is a type that can securely compare
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// a plaintext password with a hashed password
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// in constant-time. Comparers should hash the
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// plaintext password and then use constant-time
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// comparison.
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type Comparer interface {
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// Compare returns true if the result of hashing
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// plaintextPassword is hashedPassword, false
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// otherwise. An error is returned only if
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// there is a technical/configuration error.
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Compare(hashedPassword, plaintextPassword []byte) (bool, error)
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}
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// Hasher is a type that can generate a secure hash
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// given a plaintext. Hashing modules which implement
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// this interface can be used with the hash-password
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// subcommand as well as benefitting from anti-timing
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// features. A hasher also returns a fake hash which
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// can be used for timing side-channel mitigation.
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type Hasher interface {
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Hash(plaintext []byte) ([]byte, error)
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FakeHash() []byte
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}
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// Account contains a username and password.
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type Account struct {
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// A user's username.
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Username string `json:"username"`
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// The user's hashed password, in Modular Crypt Format (with `$` prefix)
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// or base64-encoded.
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Password string `json:"password"`
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password []byte
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}
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// Interface guards
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var (
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_ caddy.Provisioner = (*HTTPBasicAuth)(nil)
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_ Authenticator = (*HTTPBasicAuth)(nil)
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)
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