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2.2.1.4.21 proxy-client-agent

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This token is sent by intermediate devices (such as proxy servers) and specifies the information that the original client who initiated the HTTP request specified on the User-Agent (section 2.2.1.8) header.

Because each intermediate device replaces the information on the User-Agent header with their own information, the proxy-client-agent token enables the information on the original User-Agent header to be preserved and forwarded across possibly multiple intermediate devices to the server.

This header is defined only for requests sent to a server by an intermediate device, such as a proxy server, which is acting as a client. Intermediate devices MUST NOT modify this token if present in the request.

The syntax of the proxy-client-agent token is defined as follows.

 proxy-client-agent = "proxy-client-agent=" 
                       %x22 
                       user-agent-data 
                       %x22

Example:

 Pragma: proxy-client-agent="NSPlayer/9.0.0.0"