On top of other comments, I'll add you can do them more securely. High-assurance security often used proxies to enable support for legacy apps since the proxies

On top of other comments, I'll add you can do them more securely. High-assurance security often used proxies to enable support for legacy apps since the proxies could be clean-slated using rigorous techniques. The legacy systems were often closed-source, way too complicated, or (eg Microsoft) deliberately obfuscated. They already mentioned SSL/TLS. Another example is putting a crypto proxy in front of Microsoft Outlook that communicates with a mail guard. Can scan, encrypt, etc email with little or no work on the client. Can do (improvements here) with little to no change to (existing app) is the recurring pattern.