Headers

HTTP headers are key-value pairs that are used to pass additional information and metadata between the client and the server with an HTTP request or response. They are an essential part of the HTTP protocol, providing crucial context for how the request should be processed and how the response should be interpreted. Headers are categorized into four groups: General headers, Request headers, Response headers, and Entity headers. Request headers are sent by the client and contain more information about the resource to be fetched, or about the client itself. Common examples include: `Content-Type`, which tells the server the format of the data in the request body (e.g., `application/json`); `Authorization`, which carries credentials for authenticating the client with the server (e.g., a JWT Bearer token); and `Accept`, which tells the server which content types the client is able to understand. Response headers are sent by the server and provide additional information about the response. Common examples include: `Content-Type`, which tells the client the format of the data in the response body; `Cache-Control`, which provides caching directives for the client and proxies; and `Set-Cookie`, which is used by the server to send cookies to the client. Understanding and correctly utilizing headers is vital for building robust applications, especially for handling authentication, content negotiation, and caching.