{"id":325,"date":"2026-03-27T00:00:00","date_gmt":"2026-03-27T00:00:00","guid":{"rendered":"https:\/\/wordpress.securinsight.ca\/index.php\/2026\/03\/27\/workers-new-rfc-9440-mtls-certificate-fields-in-workers\/"},"modified":"2026-03-27T00:00:00","modified_gmt":"2026-03-27T00:00:00","slug":"workers-new-rfc-9440-mtls-certificate-fields-in-workers","status":"publish","type":"post","link":"https:\/\/wordpress.securinsight.ca\/index.php\/2026\/03\/27\/workers-new-rfc-9440-mtls-certificate-fields-in-workers\/","title":{"rendered":"Workers – New RFC 9440 mTLS certificate fields in Workers"},"content":{"rendered":"

Four new fields are now available on request.cf.tlsClientAuth<\/code> in Workers for requests that include a mutual TLS (mTLS) client certificate. These fields encode the client certificate and its intermediate chain in RFC 9440<\/a> format \u2014 the same standard format used by the Client-Cert<\/code> and Client-Cert-Chain<\/code> HTTP headers \u2014 so your Worker can forward them directly to your origin without any custom parsing or encoding logic.<\/p>\n

New fields<\/h4>\n\n\n\n\n\n\n\n\n
Field<\/th>\nType<\/th>\nDescription<\/th>\n<\/tr>\n<\/thead>\n
certRFC9440<\/code><\/td>\nString<\/td>\nThe client leaf certificate in RFC 9440 format (:base64-DER:<\/code>). Empty if no client certificate was presented.<\/td>\n<\/tr>\n
certRFC9440TooLarge<\/code><\/td>\nBoolean<\/td>\ntrue<\/code> if the leaf certificate exceeded 10 KB and was omitted from certRFC9440<\/code>.<\/td>\n<\/tr>\n
certChainRFC9440<\/code><\/td>\nString<\/td>\nThe intermediate certificate chain in RFC 9440 format as a comma-separated list. Empty if no intermediates were sent or if the chain exceeded 16 KB.<\/td>\n<\/tr>\n
certChainRFC9440TooLarge<\/code><\/td>\nBoolean<\/td>\ntrue<\/code> if the intermediate chain exceeded 16 KB and was omitted from certChainRFC9440<\/code>.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Example: forwarding client certificate headers to your origin<\/h4>\n
\n
\n
export<\/span> <\/span>default<\/span> <\/span>{<\/span><\/div><\/div>
  <\/span>async<\/span> <\/span>fetch<\/span>(<\/span>request<\/span>)<\/span> <\/span>{<\/span><\/div><\/div>
    <\/span>const<\/span> <\/span>tls<\/span> <\/span>=<\/span> <\/span>request<\/span>.<\/span>cf<\/span>.<\/span>tlsClientAuth<\/span>;<\/span><\/div><\/div>
\n<\/div><\/div>
    <\/span>\/\/ Only forward if cert was verified and chain is complete<\/span><\/div><\/div>
    <\/span>if<\/span> (<\/span>!<\/span>tls<\/span><\/span> <\/span>||<\/span> <\/span>!<\/span>tls<\/span>.<\/span>certVerified<\/span> <\/span>||<\/span> <\/span>tls<\/span>.<\/span>certRevoked<\/span> <\/span>||<\/span> <\/span>tls<\/span>.<\/span>certChainRFC9440TooLarge<\/span>) <\/span>{<\/span><\/div><\/div>
      <\/span>return<\/span> <\/span>new<\/span> <\/span>Response<\/span>(<\/span>\"Unauthorized\"<\/span>,<\/span> <\/span>{<\/span> status<\/span>:<\/span> <\/span>401<\/span> <\/span>}<\/span>)<\/span>;<\/span><\/div><\/div>
    <\/span>}<\/span><\/div><\/div>
\n<\/div><\/div>
    <\/span>const<\/span> <\/span>headers<\/span> <\/span>=<\/span> <\/span>new<\/span> <\/span>Headers<\/span>(<\/span>request<\/span>.<\/span>headers<\/span>)<\/span>;<\/span><\/div><\/div>
    <\/span><\/span>headers<\/span>.<\/span>set<\/span>(<\/span>\"Client-Cert\"<\/span>,<\/span> <\/span>tls<\/span>.<\/span>certRFC9440<\/span>)<\/span>;<\/span><\/div><\/div>
    <\/span><\/span>headers<\/span>.<\/span>set<\/span>(<\/span>\"Client-Cert-Chain\"<\/span>,<\/span> <\/span>tls<\/span>.<\/span>certChainRFC9440<\/span>)<\/span>;<\/span><\/div><\/div>
\n<\/div><\/div>
    <\/span>return<\/span> <\/span>fetch<\/span>(<\/span>new<\/span> <\/span>Request<\/span>(<\/span>request<\/span>,<\/span> <\/span>{<\/span> <\/span>headers<\/span> <\/span>}<\/span>))<\/span>;<\/span><\/div><\/div>
  <\/span>},<\/span><\/div><\/div>
};<\/span><\/div><\/div><\/code><\/pre>\n
\n
<\/div>\n<\/div>\n<\/figure>\n<\/div>\n
For more information, refer to Client certificate variables<\/a> and Mutual TLS authentication<\/a>.<\/p>","protected":false},"excerpt":{"rendered":"
Four new fields are now available on request.cf.tlsClientAuth in Workers for requests that include a mutual TLS (mTLS) client certificate. These fields encode the client certificate and its intermediate chain in RFC 9440 format \u2014 the same standard format used by the Client-Cert and Client-Cert-Chain HTTP headers \u2014 so your Worker can forward them directly […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-325","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/posts\/325","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/comments?post=325"}],"version-history":[{"count":0,"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/posts\/325\/revisions"}],"wp:attachment":[{"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/media?parent=325"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/categories?post=325"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wordpress.securinsight.ca\/index.php\/wp-json\/wp\/v2\/tags?post=325"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}