> [0]: Cloudflare provides SSL certificates to millions of web sites (even ones that don't pay us)
No, you don't. You proxy their traffic and encrypt it on the way out, undermining the security of the Web by creating a single point of failure that you've proven unable to defend.
Before using a Cloudflare product, please consider if you want to contribute to the Internet's largest man-in-the-middle attack. They have a poor track record when it comes to security[0], privacy[1], and censorship[2]. We're at the point where it's our responsibility to protect the Internet and keep these companies in check. Cloudflare is among the worst existential threats to the Internet.
To be frank, you should feel like an idiot. This was entirely foreseeable and people have been warning you not only about Slack, but about proprietary software and vendor lock-in for _literally decades_. Try not to make this mistake again. Advocate for free and open source.