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by MichaelGG 3669 days ago
But what certificate will Github present for your custom domain? I don't think you can tell CF to accept Github pages's cert for your own domain. They either use their own CA or don't do auth, right? At least on non-enterprise plans.
1 comments
manigandham 3669 days ago
CloudFlare is what serves your custom domain.

On the backend you point CloudFlare to https://username.github.io and CF will receive the wildcard certificate for *.github.io

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georgyo 3669 days ago
This is where the breakdown is. Cloudflare will get the certificate for *.github.io, however it is making the request for the custom domain. It is unable to validate the certificate.

It is impossible to enable "strict" SSL mode, because it cannot validate the certificate. And as such, a bad if able to trick cloudflare to resolve username.github.io to themselves could use any SSL certificate they choose.

This is admittedly an edge case, but in such an event, the end user would see a trusted certificate and be proxied to a bad site.

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manigandham 3669 days ago
You're right - the request to the origin will be encrypted but not fully validated since the host header will be different. It's still an encrypted connection though which is what the OP was asking about.
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MichaelGG 3669 days ago
How do you do that in CloudFlare? I didn't know you could change the host in non-enterprise versions. All I've seen is the ability to proxy request to a specific IP or CNAME.

If you CNAME your site to foo.github.com, it doesn't change the R-URI or Host header.

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2bitencryption 3669 days ago
https://www.benburwell.com/posts/configuring-cloudflare-univ...
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MichaelGG 3669 days ago
That article doesn't address what I said at all. That's showing how to disable encryption on the backend (CF to Github) by selecting "Flexible".

Looking at CF's help again and having used them a bit, there seems to be no way at all to enable full encryption (user-CF-github) with CF's non-enterprise offerings. This is because the request from CF to Github is still requested with your domain name (TLS and host header).

In order for it to work with Github's *.github.io cert, Cloudflare would need to offer an option to rewrite the request itself, not just proxy it.

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manigandham 3669 days ago
You're right that the host header wouldn't match but Cloudflare has an option to enable SSL to origin without checking for completely validated certificate. They call this Full rather than Strict: https://www.cloudflare.com/a/static/images/ssl/ssl.png

So you can still get an encrypted connection without a verified certificate.

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MichaelGG 3668 days ago
>encrypted connection without a verified certificate

Encryption doesn't work very well without authentication. In most cases any attacker with access to the medium has read+write. And without auth, you only need to, say, change DNS to insert yourself.

Opportunistic encryption is really just a last-line defence against dragnet type surveillance. Which is good, but it's hardly having end-to-end.

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dadrian 3669 days ago
That doesn't work with Github because the cert doesn't match the custom domain.
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