code: public static String getApplicationHashKey(String packageName) {
  
          String hash = "";
          try {
              PackageInfo info = QuickUtils.getContext().getPackageManager().getPackageInfo(packageName, PackageManager.GET_SIGNATURES);
              for (Signature signature : info.signatures) {
                  MessageDigest md = MessageDigest.getInstance("SHA");
                  md.update(signature.toByteArray());
                  hash = Base64.encodeToString(md.digest(), Base64.DEFAULT);
              }
          } catch (NameNotFoundException e) {
              QuickUtils.log.e("NameNotFoundException");
          } catch (NoSuchAlgorithmException e) {
              QuickUtils.log.e("NoSuchAlgorithmException");
  
          }
          return hash;
      }
docs: Your app key hash is required for example, for Facebook Login in order to
  perform security check before authorizing your app.
  
  @param packageName name of the package (e.g. "com.example.app")
  @return the application hash key