Update HTTPS config options for superagent (DefinitelyTyped#36627)

* add tls configuration types

superagent passes the ca, cert, and key parameters to `tls.createSecureContext`: https://nodejs.org/api/tls.html#tls_tls_createsecurecontext_options

* add `response` event to superagent types

types/superagent/index.d.ts

@@ -129,21 +129,22 @@ declare namespace request {
         auth(user: string, pass: string, options?: { type: 'basic' | 'auto' }): this;
         auth(token: string, options: { type: 'bearer' }): this;
         buffer(val?: boolean): this;
-        ca(cert: Buffer): this;
-        cert(cert: Buffer | string): this;
+        ca(cert: string | string[] | Buffer | Buffer[]): this;
+        cert(cert: string | string[] | Buffer | Buffer[]): this;
         clearTimeout(): this;
         end(callback?: CallbackHandler): void;
         field(name: string, val: MultipartValue): this;
         field(fields: { [fieldName: string]: MultipartValue }): this;
         get(field: string): string;
-        key(cert: Buffer | string): this;
+        key(cert: string | string[] | Buffer | Buffer[]): this;
         ok(callback: (res: Response) => boolean): this;
         on(name: 'error', handler: (err: any) => void): this;
         on(name: 'progress', handler: (event: ProgressEvent) => void): this;
+        on(name: 'response', handler: (response: Response) => void): this;
         on(name: string, handler: (event: any) => void): this;
         parse(parser: Parser): this;
         part(): this;
-        pfx(cert: Buffer | string | { pfx: Buffer, passphrase: string }): this;
+        pfx(cert: string | string[] | Buffer | Buffer[] | { pfx: string | Buffer, passphrase: string }): this;
         pipe(stream: NodeJS.WritableStream, options?: object): stream.Writable;
         query(val: object | string): this;
         redirects(n: number): this;

types/superagent/superagent-tests.ts

@@ -418,6 +418,53 @@ request
     })
     .end(callback);
 
+// HTTPS request with string, Buffer, and arrays of strings and Buffers, from: https://nodejs.org/api/tls.html#tls_tls_createsecurecontext_options
+request
+    .post('/secure')
+    .ca('ca')
+    .key('key')
+    .cert('cert')
+    .end(callback);
+
+request
+    .post('/secure')
+    .ca(['ca'])
+    .key(['key'])
+    .cert(['cert'])
+    .end(callback);
+
+request
+    .post('/secure')
+    .ca([ca])
+    .key([key])
+    .cert([cert])
+    .end(callback);
+
+request
+    .post('/secure')
+    .pfx('cert.pfx')
+    .end(callback);
+
+request
+    .post('/secure')
+    .pfx(['cert.pfx'])
+    .end(callback);
+
+request
+    .post('/secure')
+    .pfx([pfx])
+    .end(callback);
+
+// 'response' event, adapted from: https://visionmedia.github.io/superagent/docs/test.html
+request
+    .get('/user/1')
+    .on('response', res => {
+      try {
+        assert.equal('bar', res.body.foo);
+      } catch (e) { /* ignore */ }
+    })
+    .end();
+
 // ok, from: https://github.com/visionmedia/superagent/commit/34533bbc29833889090847c45a82b0ea81b2f06d
 request
     .get('/404')