Build with External Library

In order to use multipart HTTP forms, I've had to import Apache HttpClient Mime. I've tried including it in my built jar like so:

configurations {
	compile.extendsFrom(buildWith)
}

dependencies {
	minecraft 'net.minecraftforge:forge:1.15.2-31.2.0'
	buildWith 'org.apache.httpcomponents:httpmime:+'
}

jar.from {
	configurations.buildWith.collect {
		it.isDirectory() ? it : zipTree(it)
	}
}

This does add the files to the mod jar, but I still get errors when I try to use the library in game. It cannot find the class files that are being referenced.

What am I missing here? How can I include external libraries in the mod or with the game?