Django でリモート認証を行う際の注意点とは？ clean_username() メソッドの役割と詳細を徹底解説

django.contrib.auth.backends.RemoteUserBackend.clean_username() は、Django の認証バックエンド RemoteUserBackend におけるメソッドの一つです。このメソッドは、リモート認証によって取得されたユーザー名をクリーニングするために使用されます。具体的には、以下の処理を行います。

• 許可されていない文字を削除します。
• 小文字に変換します。
• 空白文字や改行文字などの不要なスペースを削除します。

詳細

RemoteUserBackend は、Web サーバーが設定した REMOTE_USER ヘッダー情報に基づいてユーザーを認証するバックエンドです。このヘッダーには、認証されたユーザーの名前が含まれています。しかし、この名前は必ずしも Django のユーザー名と一致するとは限りません。そこで、clean_username() メソッドを使用して、ユーザー名をクリーニングし、Django のユーザー名と一致する形式に変換する必要があります。

def clean_username(self, username):
    """
    Clean the username provided by the REMOTE_USER header.

    This function forces the username to lowercase, removes spaces and
    other characters that are not allowed in user names, and converts the
    username to Unicode if necessary.
    """
    username = super(RemoteUserBackend, self).clean_username(username)
    try:
        username = unicodedata.normalize('NFKD', username).encode('ascii', 'ignore').decode('ascii')
    except UnicodeDecodeError:
        pass
    username = re.sub(r'\s+', '_', username)
    username = re.sub(r'[^\w.@+-_]', '', username)
    return username.lower()

• re.sub(r'[^\w.@+-_]', '', username) は、許可されていない文字を削除する正規表現です。
• re.sub(r'\s+', '_', username) は、空白文字や改行文字などの不要なスペースをアンダースコア (_) に置き換える正規表現です。
• decode('ascii') は、ASCII 文字列を Unicode 文字列に変換するための関数です。
• encode('ascii', 'ignore') は、Unicode 文字列を ASCII 文字列に変換するための関数です。ignore パラメータは、変換できない文字を無視することを意味します。
• unicodedata.normalize('NFKD', username) は、Unicode 文字列を正規化するための関数です。

---

from django.contrib.auth.backends import RemoteUserBackend

class MyRemoteUserBackend(RemoteUserBackend):
    def clean_username(self, username):
        # Clean the username using your custom logic
        # ...

        # Call the parent class's clean_username() method to finish cleaning
        return super().clean_username(username)

# Configure Django to use your custom backend
AUTHENTICATION_BACKENDS = [
    'myapp.backends.MyRemoteUserBackend',
    # ...
]

In this example, the MyRemoteUserBackend class inherits from the RemoteUserBackend class and overrides the clean_username() method. The clean_username() method can be customized to perform any additional cleaning that is required for your application. For example, you could remove a domain name from the username, or convert the username to a specific format.

After you have created your custom backend, you need to configure Django to use it. This is done by adding the backend class to the AUTHENTICATION_BACKENDS setting in your Django settings file.

Here is an example of how to remove a domain name from the username:

def clean_username(self, username):
    # Remove the domain name from the username
    username = username.split('@')[0]

    # Call the parent class's clean_username() method to finish cleaning
    return super().clean_username(username)

In this example, the clean_username() method splits the username on the @ character and takes the first element, which is the username without the domain name. Then, it calls the parent class's clean_username() method to finish cleaning.

---

Create a custom backend

As shown in the previous example, you can create a custom backend class that inherits from the RemoteUserBackend class and overrides the clean_username() method. This gives you complete control over how the username is cleaned.

Use a custom signal

You can create a custom signal that is emitted after the user is authenticated but before the user object is saved. A receiver for this signal can then clean the username as needed.

Use a middleware

You can create a custom middleware that cleans the username before the user is authenticated. This is a good option if you need to clean the username in multiple places in your code.

Use a third-party library

There are a few third-party libraries that can be used to clean usernames. For example, the django-user-agents library can be used to remove the user agent from the username.

Which method should you use?

The best method to use depends on your specific needs. If you need complete control over how the username is cleaned, then you should create a custom backend. If you only need to perform a simple cleaning operation, then you can use a custom signal or middleware. If you need to clean the username in multiple places in your code, then you should use a third-party library.

Here is a table that summarizes the pros and cons of each method:

Method	Pros	Cons
Custom backend	Complete control over cleaning	More work to implement
Custom signal	Easy to implement	Not as flexible as a custom backend
Middleware	Easy to implement	Not as flexible as a custom backend
Third-party library	Easy to implement	May not meet your specific needs

Additional considerations

When choosing a method, you should also consider the following:

• Maintainability
  The method you choose should be easy to understand and maintain.
• Security
  The method you choose should not introduce any security vulnerabilities.
• Performance
  The method you choose should not have a significant impact on the performance of your application.