If this has been discussed to death elsewhere and
some bizarrely-informed consensus, I'll try to spare this list
my belated rantings, but this is a terrible, terrible idea.
Relying on User-Agent represents the very antithesis of
[[Postel's Law]], a rock-solid principle o which the Internet
(used to be) based.
The User-Agent request-header field contains information about the user agent originating
the request. This is for statistical purposes, the tracing of protocol violations, and
automated recognition of user agents for the sake of tailoring responses to avoid
particular user agent limitations. User agents SHOULD include this field with requests.
The field can contain multiple product tokens (section 3.8) and comments identifying the
agent and any subproducts which form a significant part of the user agent. By convention,
the product tokens are listed in order of their significance for identifying the
User-Agent = "User-Agent" ":" 1*( product | comment )
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
3. SHOULD This word, or the adjective "RECOMMENDED", mean that there
may exist valid reasons in particular circumstances to ignore a
particular item, but the full implications must be understood and
carefully weighed before choosing a different course.
I guess you just found one more implication to carefully weight before not specifying