Curl causes SSL: unable to get local issuer certificate

This looks to be a bug in homebrew's curl formula for which I have just submitted a fix. https://canvas.instructure.com/ has a certificate issued by GoDaddy and those don't seem to be working with a brewed curl that uses a brewed openssl. If/when the maintainers of homebrew accept my patch, you'll be able to simply get this fix with:

$ brew rm curl # remove your broken brewed curl
$ brew update
$ brew install --with-openssl curl

Until that happens, you can install the fix directly from my pull request like this:

$ brew rm curl # remove your broken brewed curl
$ brew install --with-openssl https://raw.githubusercontent.com/asaph/homebrew/curl-openssl-godaddy-ca-bug/Library/Formula/curl.rb

Update:

The homebrew maintainers merged my patch so the fix is officially in homebrew now. So just run the first 3 commands I described above. No need to install from the pull request anymore.