Want-Content-Digest

The HTTP Want-Content-Digest request and response header indicates 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.

Header type	Representation header
Forbidden header name	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

<algorithm>: The requested algorithm to create a digest of the message content. Only two registered digest algorithms are considered secure: sha-512 and sha-256. The insecure (legacy) registered digest algorithms are: md5, sha (SHA-1), unixsum, unixcksum, adler (ADLER32) and crc32c.
<preference>: An integer from 0 to 9 where 0 means "not acceptable", and the values 1 to 9 convey ascending, relative, weighted preference. In contrast to earlier drafts of the specifications, the weighting is not declared via q quality values.

Examples

Using Want-Content-Digest in requests

The following message asks the recipient to send a Content-Digest header using SHA-512 algorithm:

http

Want-Content-Digest: sha-512=9

Want-Content-Digest with multiple values

The following header contains three algorithms, and indicates that SHA-256 is the preferred digest algorithm that the recipient should use, followed by SHA-512, and MD5:

http

Want-Content-Digest: md5=1, sha-512=2, sha-256=3

Specifications

Specification
Digest Fields # section-4

Browser compatibility

This header has no specification-defined browser integration ("browser compatibility" does not apply). Developers can set and get HTTP headers using fetch() in order to provide application-specific implementation behavior.