Electron Builder Code Signing Download Certificate Error

I'm building an Electron app and using the npm package electron-builder to build the app and installer for Windows. I'm trying to use the

and environment variables to sign the app as described here: https://github.com/electron-userland/electron-builder#travis-appveyor-and-other-ci-servers

On first try the error and stack trace is:

Unhandled rejection Error: unable to verify the first certificate

at Error (native)

at TLSSocket.<anonymous> (_tls_wrap.js:1065:38)

at emitNone (events.js:80:13)

at TLSSocket.emit (events.js:179:7)

at TLSSocket._init.ssl.onclienthello.ssl.oncertcb.TLSSocket._finishInit (_tls_wrap.js:593:8)

at TLSWrap.ssl.onclienthello.ssl.oncertcb.ssl.onnewsession.ssl.onhandshakedone (_tls_wrap.js:425:38)

From previous event:

at Object.downloadCertificate (C:\projects\presentation\Electron\node_modules\electron-builder\src\codeSign.ts:97:18)

...

I then tried setting the environment variable and now get a different error:

Unhandled rejection Error: Request error, status 400: Bad Request

at ClientRequest.<anonymous> (C:\projects\presentation\Electron\node_modules\electron-builder\src\httpRequest.ts:36:16)

...

The particular line that is being called in electron-builder's appears to just be using Node's https module: https://github.com/electron-userland/electron-builder/blob/master/src/httpRequest.ts#L28

This leads me to believe there is something up with the Windows machine or certificates. I'm running this on Windows 10, node 5.9.0.