ACL configuration based on request method and request header in Nginx reverse proxy

Nginx is a lightweight and efficient web server that is increasingly used in building modern web applications. Its reverse proxy function allows Nginx to be used for load balancing, caching, open source API gateway and other purposes. This article will focus on ACL (access control list) configuration based on request method and request header.

ACL is a mechanism used to control access and is widely used in Nginx. Through ACL, Nginx can filter and verify requests and then distribute them to the target server. The ACL mechanism mainly consists of three parts: variables, operators and values.

Variables are some information in the request, such as request headers, request methods, request parameters, etc. Nginx can check the values ​​of these variables to determine whether to send the request to the server. Value refers to the data that the variable is compared to. Operators specify how variables and values ​​are compared.

Nginx supports ACL configuration based on request methods and request headers. You may want to use these configurations in the following situations:

1. You want to filter requests based on the type of request method, such as GET, POST, DELETE, etc.
2. You want to filter requests based on request headers, such as Authorization, Content-Type, etc. This may be commonly used in API gateways to check client authorization and maintain necessary security for the application.

Configuring ACL based on request method

Configuring ACL based on request method is very simple. You need to use the variable $request_method, define an operator to check the value of this variable, and then specify a list of allowed request methods. The following is an example:

location /api {
  if ($request_method !~ ^(GET|POST|PUT)$ ) {
    return 405;
  }
  proxy_pass http://localhost:8080;
}

This configuration means that if the request method is not GET, POST, or PUT, HTTP status 405 ("Method Not Allowed") is returned. If request methods other than GET, POST or PUT are matched here, Nginx will not send them to the proxy server.

ACL configuration based on request header

ACL configuration based on request header is similar to configuration based on request method. You can get the header information in the request by using the variable $http_ plus the name of the request header. You can then use an operator to check the value of the header using a method similar to the request-based approach. For example:

location /api {
  if ($http_authorization !~* "Bearer [a-zA-Z0-9]+" ) {
    return 401;
  }
  proxy_pass http://localhost:8080;
}

In the above configuration, if the request header Authorization does not contain an authorization tag starting with Bearer, HTTP status 401 ("Unauthorized") will be returned. Therefore, Nginx will not send any requests to the proxy server except for the correct authorization header.

Summary

Nginx’s ACL functionality can be used to perform a lot of request-related logic. ACL configuration based on request method and request header is an effective method to implement access control in specific scenarios. Additionally, you can combine it with other Nginx features, such as logging and rate limiting, to enhance the security and performance of your web application.

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