Allowing an unescaped "/" or other special character in the key file path, key file password, or the certificate authority file path introduces a parsing ambiguity. It violates the Connection String Spec's algorithm, which requires a driver to parse hostnames and user info from the URI segment before the last "/" character, and requires the driver to parse the options from the segment after the last "/" character. Thus we can't correctly parse a URI like this without violating the spec:

"mongodb://server/?sslclientcertificatekeyfile=/tmp/key.pem"

We can't parse that string while conforming to the spec, because the segment before the last "/" character is this:

"mongodb://server/?sslclientcertificatekeyfile=/tmp"

Instead, we must require this syntax:

"mongodb://server/?sslclientcertificatekeyfile=%2Ftmp%2Fkey.pem"