This is a side-effect of us using JavaScript APIs instead of Python TLS and setting is_verified on the EmscriptenHTTPConnection so urllib3 is emitting an InsecureRequestWarning for every request, even ones that are using HTTPS.

• Set the proper value of is_verified depending on whether the request is HTTP or HTTPS.
• Add a test case that asserts that an InsecureRequestWarning is emitted for HTTP and isn't emitted for HTTPS.