HTTP Headers
Want Content Digest
HTTP Header
The HTTP Want-Content-Digest request and response headers indicate a preference for the recipient to send a Content-Digest integrity header in messages associated with the request URI and representation metadata.
The header includes hashing algorithm preferences that the recipient can use in subsequent messages.
The preferences only serve as a hint, and the recipient may ignore the algorithm choices, or the integrity headers entirely.
Some implementations may send unsolicited Content-Digest headers without requiring a Want-Content-Digest header in a previous message.
The relevant details concerning header types are summarized below:
Representation header
Forbidden request header: No
Syntax
A comma-separated list of one or more hashing algorithms:
http
Want-Content-Digest: <algorithm>=<preference>
Want-Content-Digest: <algorithm>=<preference>, …, <algorithmN>=<preferenceN>
Directives
Directives
- <algorithm>
The specified algorithm used to generate a message digest. Only two digest algorithms are considered secure:
sha-512andsha-256. The insecure (legacy) algorithms include:md5,sha (SHA-1),unixsum,unixcksum,adler(ADLER32), andcrc32c.- <preference>
An integer from 0 to 9 indicating preference where
0means "not acceptable". Values from1to9indicate increasing preference. Unlike earlier drafts, the preference weights are not expressed viaqquality values.
Example
Examples
The following message requests the recipient to include a <Content-Digest> header using the SHA-512 algorithm:
Want-Content-Digest: sha-512=9
The header below specifies three algorithms, with SHA-256 as the preferred digest algorithm for the recipient to use, followed by SHA-512 and MD5:
Want-Content-Digest: md5=1, sha-512=2, sha-256=3
This header does not have a standard browser integration (“browser compatibility” does not apply).
Developers can set and retrieve HTTP headers using fetch() in order to implement application-specific behavior.
How to Modify Header using Requestly
Requestly is a powerful Chrome extension that allows you to modify HTTP headers, including the Want Content Digest header. This is especially useful for testing how your application handles content integrity checks or debugging issues related to content verification. Steps to Modify the Want Content Digest Header:
- Install and open the Requestly Chrome extension. You can find it on the Chrome Web Store.
- Create a new rule: Click on “Create Rule” and choose “Modify Headers” from the list of available rule types.
- Add a new header modification:
- Under “Action”, select “Add” or “Override”.
- In the “Header Name” field, enter Want Content Digest.
- In the “Header Value” field, enter the desired digest algorithm or value (e.g., sha-256).
- Set the URL condition: Specify the URL or pattern where this header change should apply (e.g., https://your-api.com/*).
- Save the rule.
Once set up, Requestly will inject the Want Content Digest header into all matching requests, allowing you to test how your server validates content digests or simulate client requests needing content integrity checks.
Modifying the Want Content Digest header helps you verify that your server correctly handles content integrity validation, which is important to ensure data hasn’t been tampered with during transfer. It also helps developers test different digest algorithms to improve security or debug related issues easily.
Table of Contents
- No headings found.
