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HTTP はアクセス制御と認証の基本的な枠組みを提供しています。最も一般的な HTTP 認証は、 "Basic" 認証に基づいています。このページでは、 HTTP の認証の枠組みを紹介し、サーバーで HTTP の "Basic" 認証を使用してアクセスを制限する方法を紹介します。
一般的な HTTP 認証の枠組み
RFC 7235 defines the HTTP authentication framework which can be used by a server to challenge a client request and by a client to provide authentication information. The challenge and response flow works like this: The server responds to a client with a 401 (Unauthorized) response status and provides information on how to authorize with a WWW-Authenticate response header containing at least one challenge. A client that wants to authenticate itself with a server can then do so by including an Authorization request header field with the credentials. Usually a client will present a password prompt to the user and will then issue the request including the correct Authorization header.
In the case of a "Basic" authentication like shown in the figure, the exchange must happen over an HTTPS (TLS) connection to be secure.
プロキシ認証
The same challenge and response mechanism can be used for proxy authentication. In this case, it is an intermediate proxy that requires authentication. As both resource authentication and proxy authentication can coexist, a different set of headers and status codes is needed. In the case of proxies, the challenging status code is 407 (Proxy Authentication Required), the Proxy-Authenticate response header contains at least one challenge applicable to the proxy, and the Proxy-Authorization request header is used for providing the credentials to the proxy server.
アクセスの不許可
If a (proxy) server receives valid credentials that are not adequate to gain access for a given resource, the server should respond with the 403 Forbidden status code. Unlike 401 Unauthorized or 407 Proxy Authentication Required, authentication is impossible for this user.
オリジン間の画像の認証
A potential security hole that has recently been fixed by browsers is authentication of cross-site images. From Firefox 59 onwards, image resources loaded from different origins to the current document are no longer able to trigger HTTP authentication dialogs (バグ 1423146), preventing user credentials being stolen if attackers were able to embed an arbitrary image into a third-party page.
HTTP 認証の文字エンコーディング
Browsers use utf-8 encoding for usernames and passwords. Firefox used to use ISO-8859-1, but changed over to utf-8 for parity with other browsers, and to avoid potential problems as described in バグ 1419658.
WWW-Authenticate 及び Proxy-Authenticate ヘッダー
The WWW-Authenticate and Proxy-Authenticate response headers define the authentication method that should be used to gain access to a resource. They need to specify which authentication scheme is used, so that the client that wishes to authorize knows how to provide the credentials. The syntax for these headers is the following:
WWW-Authenticate: <type> realm=<realm> Proxy-Authenticate: <type> realm=<realm>
Here, <type> is the authentication scheme ("Basic" is the most common scheme and introduced below). The realm is used to describe the protected area or to indicate the scope of protection. This could be a message like "Access to the staging site" or similar, so that the user knows to which space they are trying to get access to.
Authorization 及び Proxy-Authorization ヘッダー
The Authorization and Proxy-Authorization request headers contain the credentials to authenticate a user agent with a (proxy) server. Here, the type is needed again followed by the credentials, which can be encoded or encrypted depending on which authentication scheme is used.
Authorization: <type> <credentials> Proxy-Authorization: <type> <credentials>
認証方式
The general HTTP authentication framework is used by several authentication schemes. Schemes can differ in security strength and in their availability in client or server software.
The most common authentication scheme is the "Basic" authentication scheme which is introduced in more details below. IANA maintains a list of authentication schemes, but there are other schemes offered by host services, such as Amazon AWS. Common authentication schemes include:
- Basic (see RFC 7617, base64-encoded credentials. See below for more information.),
- Bearer (see RFC 6750, bearer tokens to access OAuth 2.0-protected resources),
- Digest (see RFC 7616, only md5 hashing is supported in Firefox, see バグ 472823 for SHA encryption support),
- HOBA (see RFC 7486 (draft), HTTP Origin-Bound Authentication, digital-signature-based),
- Mutual (see draft-ietf-httpauth-mutual),
-
AWS4-HMAC-SHA256 (see AWS docs).
Basic 認証方式
The "Basic" HTTP authentication scheme is defined in RFC 7617, which transmits credentials as user ID/password pairs, encoded using base64.
Basic 認証の安全性
As the user ID and password are passed over the network as clear text (it is base64 encoded, but base64 is a reversible encoding), the basic authentication scheme is not secure. HTTPS / TLS should be used in conjunction with basic authentication. Without these additional security enhancements, basic authentication should not be used to protect sensitive or valuable information.
Apache 及び Basic 認証によるアクセス制限
To password-protect a directory on an Apache server, you will need a .htaccess and a .htpasswd file.
The .htaccess file typically looks like this:
AuthType Basic AuthName "Access to the staging site" AuthUserFile /path/to/.htpasswd Require valid-user
The .htaccess file references a .htpasswd file in which each line contains of a username and a password separated by a colon (":"). You can not see the actual passwords as they are encrypted (md5 in this case). Note that you can name your .htpasswd file differently if you like, but keep in mind this file shouldn't be accessible to anyone. (Apache is usually configured to prevent access to .ht* files).
aladdin:$apr1$ZjTqBB3f$IF9gdYAGlMrs2fuINjHsz. user2:$apr1$O04r.y2H$/vEkesPhVInBByJUkXitA/
nginx 及び Basic 認証によるアクセス制限
For nginx, you will need to specify a location that you are going to protect and the auth_basic directive that provides the name to the password-protected area. The auth_basic_user_file directive then points to a .htpasswd file containing the encrypted user credentials, just like in the Apache example above.
location /status {
auth_basic "Access to the staging site";
auth_basic_user_file /etc/apache2/.htpasswd;
}
URL 内の認証情報を使用したアクセス
Many clients also let you avoid the login prompt by using an encoded URL containing the username and the password like this:
https://username:password@www.example.com/
The use of these URLs is deprecated. In Chrome, the username:password@ part in URLs is even stripped out for security reasons. In Firefox, it is checked if the site actually requires authentication and if not, Firefox will warn the user with a prompt "You are about to log in to the site “www.example.com” with the username “username”, but the website does not require authentication. This may be an attempt to trick you."