Session 'app': Error Installing APK

01/18 16:20:47: Launching app
$ adb push E:hwahwaappbuildoutputsapkdebugapp-debug.apk /data/local/tmp/com.hwa
com.android.ddmlib.AdbCommandRejectedException: device unauthorized.
This adb server's $ADB_VENDOR_KEYS is not set
Try 'adb kill-server' if that seems wrong.
Otherwise check for a confirmation dialog on your device.
Error while Installing APK