challenge-response calculation function

app/scripts/comp/app/yubikey.js

@@ -192,17 +192,26 @@ const YubiKey = {
     },
 
     getOtp(serial, entry, callback) {
-        if (this.process) {
-            return callback('Already in progress');
-        }
-        this.aborted = false;
-
         return Launcher.spawn({
             cmd: 'ykman',
             args: ['-d', serial, 'oath', 'code', '--single', entry],
             noStdOutLogging: true,
             complete: (err, stdout) => {
-                this.process = null;
+                if (err) {
+                    return callback(err);
+                }
+                const otp = stdout.trim();
+                callback(null, otp);
+            }
+        });
+    },
+
+    calculateChalResp(serial, slot, challenge, callback) {
+        return Launcher.spawn({
+            cmd: 'ykman',
+            args: ['-d', serial, 'otp', 'calculate', slot, challenge],
+            noStdOutLogging: true,
+            complete: (err, stdout) => {
                 if (err) {
                     return callback(err);
                 }