http: authentication module; hash-password cmd; http_basic provider

This implements HTTP basicauth into Caddy 2. The basic auth module will
not work with passwords that are not securely hashed, so a subcommand
hash-password was added to make it convenient to produce those hashes.

Also included is Caddyfile support.

Closes #2747.

1 files changed, 164 insertions, 0 deletions

diff --git a/modules/caddyhttp/caddyauth/basicauth.go b/modules/caddyhttp/caddyauth/basicauth.go
new file mode 100644
index 0000000..b7c002b
--- /dev/null
+++ b/modules/caddyhttp/caddyauth/basicauth.go
@@ -0,0 +1,164 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package caddyauth
+
+import (
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+func init() {
+	caddy.RegisterModule(HTTPBasicAuth{})
+}
+
+// HTTPBasicAuth facilitates HTTP basic authentication.
+type HTTPBasicAuth struct {
+	HashRaw     json.RawMessage `json:"hash,omitempty"`
+	AccountList []Account       `json:"accounts,omitempty"`
+	Realm       string          `json:"realm,omitempty"`
+
+	Accounts map[string]Account `json:"-"`
+	Hash     Comparer           `json:"-"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (HTTPBasicAuth) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		Name: "http.handlers.authentication.providers.http_basic",
+		New:  func() caddy.Module { return new(HTTPBasicAuth) },
+	}
+}
+
+// Provision provisions the HTTP basic auth provider.
+func (hba *HTTPBasicAuth) Provision(ctx caddy.Context) error {
+	if hba.HashRaw == nil {
+		return fmt.Errorf("passwords must be hashed, so a hash must be defined")
+	}
+
+	// load password hasher
+	hashIface, err := ctx.LoadModuleInline("algorithm", "http.handlers.authentication.hashes", hba.HashRaw)
+	if err != nil {
+		return fmt.Errorf("loading password hasher module: %v", err)
+	}
+	hba.Hash = hashIface.(Comparer)
+	hba.HashRaw = nil // allow GC to deallocate
+
+	if hba.Hash == nil {
+		return fmt.Errorf("hash is required")
+	}
+
+	// load account list
+	hba.Accounts = make(map[string]Account)
+	for _, acct := range hba.AccountList {
+		if _, ok := hba.Accounts[acct.Username]; ok {
+			return fmt.Errorf("username is not unique: %s", acct.Username)
+		}
+		hba.Accounts[acct.Username] = acct
+	}
+	hba.AccountList = nil // allow GC to deallocate
+
+	return nil
+}
+
+// Authenticate validates the user credentials in req and returns the user, if valid.
+func (hba HTTPBasicAuth) Authenticate(w http.ResponseWriter, req *http.Request) (User, bool, error) {
+	username, plaintextPasswordStr, ok := req.BasicAuth()
+
+	// if basic auth is missing or invalid, prompt for credentials
+	if !ok {
+		// browsers show a message that says something like:
+		// "The website says: <realm>"
+		// which is kinda dumb, but whatever.
+		realm := hba.Realm
+		if realm == "" {
+			realm = "restricted"
+		}
+
+		w.Header().Set("WWW-Authenticate", fmt.Sprintf(`Basic realm="%s"`, realm))
+
+		return User{}, false, nil
+	}
+
+	plaintextPassword := []byte(plaintextPasswordStr)
+
+	account, accountExists := hba.Accounts[username]
+	// don't return early if account does not exist; we want
+	// to try to avoid side-channels that leak existence
+
+	same, err := hba.Hash.Compare(account.Password, plaintextPassword, account.Salt)
+	if err != nil {
+		return User{}, false, err
+	}
+	if !same || !accountExists {
+		return User{}, false, nil
+	}
+
+	return User{ID: username}, true, nil
+}
+
+// Comparer is a type that can securely compare
+// a plaintext password with a hashed password
+// in constant-time. Comparers should hash the
+// plaintext password and then use constant-time
+// comparison.
+type Comparer interface {
+	// Compare returns true if the result of hashing
+	// plaintextPassword with salt is hashedPassword,
+	// false otherwise. An error is returned only if
+	// there is a technical/configuration error.
+	Compare(hashedPassword, plaintextPassword, salt []byte) (bool, error)
+}
+
+type quickComparer struct{}
+
+func (quickComparer) Compare(theirHash, plaintext, _ []byte) (bool, error) {
+	ourHash := quickHash(plaintext)
+	return hashesMatch(ourHash, theirHash), nil
+}
+
+func hashesMatch(pwdHash1, pwdHash2 []byte) bool {
+	return subtle.ConstantTimeCompare(pwdHash1, pwdHash2) == 1
+}
+
+// quickHash returns the SHA-256 of v. It
+// is not secure for password storage, but
+// it is useful for efficiently normalizing
+// the length of plaintext passwords for
+// constant-time comparisons.
+//
+// Errors are discarded.
+func quickHash(v []byte) []byte {
+	h := sha256.New()
+	h.Write([]byte(v))
+	return h.Sum(nil)
+}
+
+// Account contains a username, password, and salt (if applicable).
+type Account struct {
+	Username string `json:"username"`
+	Password []byte `json:"password"`
+	Salt     []byte `json:"salt,omitempty"` // for algorithms where external salt is needed
+}
+
+// Interface guards
+var (
+	_ caddy.Provisioner = (*HTTPBasicAuth)(nil)
+	_ Authenticator     = (*HTTPBasicAuth)(nil)
+)