As we have been discussing this week, securing the connection between Cloudflare and the origin server is arguably just as important as securing the connection between end users and Cloudflare. The origin certificate authority we announced this week will help CloudFlare verify that it is talking to the correct origin server. But what about verification in the opposite direction? How can the origin verify that the client talking to it is actually CloudFlare?
TLS Client Authentication
TLS (the modern version of SSL) allows a client to verify the identity of the server it is talking to. Normally, a TLS handshake is one-way, that is, the client is able to verify the server's identity, but the server is not able to verify the client's identity. What about when both sides need to verify each other's identity?
Enter TLS Client Authentication. In a client authenticated TLS handshake both sides provide a certificate to be verified. If the origin server is configured to only accept requests which use a valid client certificate from Cloudflare, requests which have not passed through Cloudflare will be dropped (as they will not have our certificate). This means that attackers cannot circumvent CloudFlare features such as our WAF, even via an attack like TCP source IP spoofing which could typically be used make an origin server believe malicious requests have passed through CloudFlare's network.
To implement TLS client authentication in Cloudflare, one of our engineers, Piotr Sikora, added support to nginx. This code is open source and has been merged into the official nginx 1.7 branch, and can be used by anyone utilizing nginx's proxy module.
Enabling Authenticated Origin Pulls
Generally, enabling Authenticated Origin Pulls does not cause any problems with a website, even if client certificates are not validated. However, in the event a website uses client certificates for other purposes, the Cloudflare origin-pull certificate may conflict and cause problems. Consequently, Authenticated Origin Pulls are an opt-in setting for Cloudflare customers. This service is available for all levels of Cloudflare plan: Free, Professional, Business, and Enterprise.
In order to enable Authenticated Origin Pulls for your Cloudflare protected website, you will need to use our new dashboard (currently in beta). To access this beta dashboard, first log in to your Cloudflare account. In the lower right corner of the page there is a button labeled "Try Our New Dashboard." Click and log in again. At this point, you're in our new dashboard with access to all your existing domains and settings through a completely new user interface.
There will be more information about this new dashboard in the near future, but feel free to check it out. You can continue to freely switch between old and new dashboard.
Cloudflare presents certificates signed by a CA with the following certificate:
-----BEGIN CERTIFICATE----- MIIGBjCCA/CgAwIBAgIIV5G6lVbCLmEwCwYJKoZIhvcNAQENMIGQMQswCQYDVQQG EwJVUzEZMBcGA1UEChMQQ2xvdWRGbGFyZSwgSW5jLjEUMBIGA1UECxMLT3JpZ2lu IFB1bGwxFjAUBgNVBAcTDVNhbiBGcmFuY2lzY28xEzARBgNVBAgTCkNhbGlmb3Ju aWExIzAhBgNVBAMTGm9yaWdpbi1wdWxsLmNsb3VkZmxhcmUubmV0MB4XDTE1MDEx MzAyNDc1M1oXDTIwMDExMjAyNTI1M1owgZAxCzAJBgNVBAYTAlVTMRkwFwYDVQQK ExBDbG91ZEZsYXJlLCBJbmMuMRQwEgYDVQQLEwtPcmlnaW4gUHVsbDEWMBQGA1UE BxMNU2FuIEZyYW5jaXNjbzETMBEGA1UECBMKQ2FsaWZvcm5pYTEjMCEGA1UEAxMa b3JpZ2luLXB1bGwuY2xvdWRmbGFyZS5uZXQwggIiMA0GCSqGSIb3DQEBAQUAA4IC DwAwggIKAoICAQDdsts6I2H5dGyn4adACQRXlfo0KmwsN7B5rxD8C5qgy6spyONr WV0ecvdeGQfWa8Gy/yuTuOnsXfy7oyZ1dm93c3Mea7YkM7KNMc5Y6m520E9tHooc f1qxeDpGSsnWc7HWibFgD7qZQx+T+yfNqt63vPI0HYBOYao6hWd3JQhu5caAcIS2 ms5tzSSZVH83ZPe6Lkb5xRgLl3eXEFcfI2DjnlOtLFqpjHuEB3Tr6agfdWyaGEEi lRY1IB3k6TfLTaSiX2/SyJ96bp92wvTSjR7USjDV9ypf7AD6u6vwJZ3bwNisNw5L ptph0FBnc1R6nDoHmvQRoyytoe0rl/d801i9Nru/fXa+l5K2nf1koR3IX440Z2i9 +Z4iVA69NmCbT4MVjm7K3zlOtwfI7i1KYVv+ATo4ycgBuZfY9f/2lBhIv7BHuZal b9D+/EK8aMUfjDF4icEGm+RQfExv2nOpkR4BfQppF/dLmkYfjgtO1403X0ihkT6T PYQdmYS6Jf53/KpqC3aA+R7zg2birtvprinlR14MNvwOsDOzsK4p8WYsgZOR4Qr2 gAx+z2aVOs/87+TVOR0r14irQsxbg7uP2X4t+EXx13glHxwG+CnzUVycDLMVGvuG aUgF9hukZxlOZnrl6VOf1fg0Caf3uvV8smOkVw6DMsGhBZSJVwao0UQNqQIDAQAB o2YwZDAOBgNVHQ8BAf8EBAMCAAYwEgYDVR0TAQH/BAgwBgEB/wIBAjAdBgNVHQ4E FgQUQ1lLK2mLgOERM2pXzVc42p59xeswHwYDVR0jBBgwFoAUQ1lLK2mLgOERM2pX zVc42p59xeswCwYJKoZIhvcNAQENA4ICAQDKDQM1qPRVP/4Gltz0D6OU6xezFBKr LWtDoA1qW2F7pkiYawCP9MrDPDJsHy7dx+xw3bBZxOsK5PA/T7p1dqpEl6i8F692 g//EuYOifLYw3ySPe3LRNhvPl/1f6Sn862VhPvLa8aQAAwR9e/CZvlY3fj+6G5ik 3it7fikmKUsVnugNOkjmwI3hZqXfJNc7AtHDFw0mEOV0dSeAPTo95N9cxBbm9PKv qAEmTEXp2trQ/RjJ/AomJyfA1BQjsD0j++DI3a9/BbDwWmr1lJciKxiNKaa0BRLB dKMrYQD+PkPNCgEuojT+paLKRrMyFUzHSG1doYm46NE9/WARTh3sFUp1B7HZSBqA kHleoB/vQ/mDuW9C3/8Jk2uRUdZxR+LoNZItuOjU8oTy6zpN1+GgSj7bHjiy9rfA F+ehdrz+IOh80WIiqs763PGoaYUyzxLvVowLWNoxVVoc9G+PqFKqD988XlipHVB6 Bz+1CD4D/bWrs3cC9+kk/jFmrrAymZlkFX8tDb5aXASSLJjUjcptci9SKqtI2h0J wUGkD7+bQAr+7vr8/R+CBmNMe7csE8NeEX6lVMF7Dh0a1YKQa6hUN18bBuYgTMuT QzMmZpRpIBB321ZBlcnlxiTJvWxvbCPHKHj20VwwAz7LONF59s84ZsOqfoBv8gKM s0s5dsq5zpLeaw== -----END CERTIFICATE-----
This certificate is also available from https://origin-pull.cloudflare.com/
Origin Server Configuration
We will include configuration examples for popular web servers in our Cloudflare Support Docs in the next week.