Support HTTPS (SSL) for "koop serve" command

[gavinr]

For development workflows where you're working on a provider and using the koop-cli to run a dev/debug environment, it would be valuable to have the option to have the server that runs when you run koop serve to support HTTPS/SSL. This is because more places (now notably the ArcGIS Online Map Viewer) are enforcing HTTPS even for development workflows.

[gavinr]

Workaround when you're in a provider add-in:

1. Generate a self signed certificate: server.cert and server.key files and place them in the root directory.
2. Create a new file test/server.js with contents:

   const Koop = require("koop");
   const fs = require("fs");
   const https = require("https");
   // require the src directory
   const testProvider = require("../src/index");
   // initiate a koop app
   const koop = new Koop();
   // register koop plugins
   koop.register(testProvider);
   // start the server
   https
     .createServer(
       {
         key: fs.readFileSync("server.key"),
         cert: fs.readFileSync("server.cert"),
       },
       koop.server
     )
     .listen(3000, function () {
       console.log(
         "Example app listening on port 3000! Go to https://localhost:3000/"
       );
     });

3. Change the npm start command to be koop serve test/server.js --debug --watch

(thanks to @haoliangyu for this example)

[haoliangyu]

It is valuable to provide an optional HTTPS dev server, particularly when working with Esri products.

Since it is simply to create one with ssh cert and key files, I see it possible to add two options in the serve command:

koop serve --ssh-cert=<path-to-cert> --ssh-key=<path-to-key>

When both options are set, a HTTPS server will be started instead.

[haoliangyu]

@gavinr The update is out at v1.1.0.