Accept-Signature specifies a syntax that violates the ABNF for sh-param-list

[CBonnell]

The Accept-Signature header (section 3.7) is defined as a sh-param-list. It also specifies that identifiers can be specified with a leading hyphen ("-") to denote a lack of support.

However, the leading hyphen violates the ABNF for sh-param-list and identifier as defined in https://tools.ietf.org/html/draft-ietf-httpbis-header-structure-07. Notably, sh-param-list has no provision to allow hyphens before the "identifier" (https://tools.ietf.org/html/draft-ietf-httpbis-header-structure-07#section-3.3) and the identifier (https://tools.ietf.org/html/draft-ietf-httpbis-header-structure-07#section-3.8) must begin with a lowercase letter.