sdkmanager's Proxy Host Field Is Not a Login Field
The documented host and port options identify an endpoint. They do not turn a username-bearing string into a supported authentication exchange.
--proxy_host expects a proxy hostname or address. Putting username:password@host there is not the same as supplying a hostname plus a supported authentication method.
The sdkmanager reference documents proxy type, host, and port options. Check the installed tool's documented authentication support separately. A flag accepted by another Java program is not automatically an SDK Manager feature.
In particular, setting arbitrary properties named http.proxyUser or http.proxyPassword does not prove that the downloader reads them. An authentication mechanism must actually consume the account and perform the required exchange.
Also keep --no_https out of a login repair. Changing how a download is requested does not supply missing proxy credentials.
If the supported client cannot meet the proxy's authentication requirement, use the organization's approved compatible access arrangement. Keep the service's endpoint, account mechanism, and download TLS policy as separate configuration decisions. An approved unauthenticated route to public SDK downloads can take its HTTP host and port from the HTTP proxy list; it does not add authentication support for the original service.