How can I detect if the back button is virtual or physical? Hardware or Software Device buttons

Solution for Android Only:

Ok I succeeded I do believe. Took 2 days of melting my brain trying to work through all the problems i encountered along the way.

This class interacts with the Plugin and calls its methods.

 using UnityEngine;
 using System.Collections;
 using System.IO;
 
 public class AccessButtonsType : MonoBehaviour{
 #if UNITY_ANDROID
   private AndroidJavaObject testobj = null;
     private AndroidJavaObject playerActivityContext = null;
  
     void Start() {
         if (testobj == null) {
             // First, obtain the current activity context
             using (var actClass = new AndroidJavaClass("com.unity3d.player.UnityPlayer")) {
                 playerActivityContext = actClass.GetStatic<AndroidJavaObject>("currentActivity");
             }
  
             // Pass the context to a newly instantiated UnityGetButtonsType object
             using (var pluginClass = new AndroidJavaClass("com.tmg.getbuttons.UnityGetButtonsType")) {
                 if (pluginClass != null) {
                     testobj = pluginClass.CallStatic<AndroidJavaObject>("instance");
                     testobj.Call("setContext", playerActivityContext);
                 }
             }
         }
     }
   
   public static string GetButtonsT() {
     string emptyString = null;
     if( Application.platform != RuntimePlatform.Android )
       return emptyString;
 
     var pluginClass = new AndroidJavaClass("com.tmg.getbuttons.UnityGetButtonsType") ;
     AndroidJavaObject plugin = pluginClass.CallStatic<AndroidJavaObject>("instance");
     return plugin.Call<string>("GetButtonsType");
   } 
   #endif
 }

I threw this in to test and control the .cs class.

 using UnityEngine;
 using System.Collections;
 
 public class AccessScript : MonoBehaviour {
     
     public string isIt;
     void Start ()
     {
         isIt = "Empty";
     }
     
     void Update ()
     {
         isIt = AccessButtonsType.GetButtonsT();
         if(isIt == null)
             isIt = "Empty";
         Debug.Log(isIt);
     }
 
     void OnGUI()
     {
         GUI.Label(new Rect(10, 10, 100, 20), isIt + " Buttons");
     }
 }

This is the .java plugin I compiled in Android studio and dropped into the Plugins/Android folder in .jar format. I didnt need to target JDK 1.6. I didn't need any XML manifest in the plugins folder.

 package com.tmg.getbuttons;
 
 import android.content.ContentValues;
 import android.content.Intent;
 import android.content.Context;
 import android.os.Environment;
 import android.view.ViewConfiguration;
 
 public class UnityGetButtonsType {
 
     Context context;
     private static UnityGetButtonsType m_instance;
 
     public static UnityGetButtonsType instance() {
         if(m_instance == null)
             m_instance = new UnityGetButtonsType();
         return m_instance;
     }
 
     public UnityGetButtonsType(){
         m_instance = this;
     }
 
     public void setContext(Context ctx) {
         this.context = ctx;
     }
 
     public String GetButtonsType() {
         ViewConfiguration vConfig = ViewConfiguration.get(this.context);
 
         if (vConfig.hasPermanentMenuKey()) {
             return "hard";
         } else {
             return "soft";
         }
     }
 }