Swift is “a high-performance system programming language [with] a clean and modern syntax”. It is the standard language for native application development on Apple’s platforms.
(This guide also essentially applies to Objective-C.)
In Swift, TLS certificates are accessed in three main ways:
URLSession in Foundation)NWConnection in Network.framework)Sec... APIs in Security.framework)On macOS, Swift uses Apple’s implementations of these frameworks. Apple’s implementations leverage the Keychain internally.
Therefore, Swift supports the system truststore on macOS. This the default behaviour; you do not need to do anything extra to use it.
On Windows, Swift is built with open source implementations of these frameworks. For example, swift-corelibs-foundation reimplements Foundation. That library uses Curl as its HTTPS driver, and on Windows, it builds Curl with the Schannel backend (source: apple/swift-corelibs-foundation#4625).
Therefore, Swift supports the system truststore on Windows. This the default behaviour; you do not need to do anything extra to use it.
A small number of Swift apps may use different networking libraries (e.g. Boost.ASIO), particularly if they are built around a cross-platform C library for code sharing. These apps depend on the networking library supporting native TLS certificate verification.