Allow for 2FA to be disabled

sections/user/edit.php

           <? $TwoFASecret = empty($TwoFactor) ? $TwoFA->createSecret() : $TwoFactor; ?>
           <div class="field_div">
             <? if (!empty($TwoFactor)) { ?>
-            <p>2FA is enabled for this account with the following secret:</p>
+            <p class="min_padding">2FA is enabled for this account with the following secret:</p>
             <? } ?>
             <img src="<?=$TwoFA->getQRCodeImageAsDataUri(SITE_NAME, $TwoFASecret)?>">
             <input type="text" size="20" name="twofasecret" id="twofasecret" value="<?=$TwoFASecret?>" readonly><br>
             <input type="text" size="20" maxlength="6" name="twofa" id="twofa" placeholder="Verification Code">
             <p class="min_padding">To enable 2FA, scan the above QR code (or add the secret below it) to your 2FA client of choice, and enter a verification code it generates. Note that the verification code must not have expired when you save your profile.</p>
             <p class="min_padding">When setting up 2FA, you must enter your current password in the "Current password" field before saving your changes.</p>
+            <p class="min_padding"><strong class="important_text">WARNING</strong>: Losing your 2FA key can make your account unrecoverable. Only enable it if you're sure you can handle it.
+            <? } else { ?>
+            <label><input type="checkbox" name="disable2fa" id="disable2fa" />
+            Disable 2FA</label>
+            <p class="min_padding">When disabling 2FA, you must enter your current password in the "Current Password" field before saving your changes</p>
             <? } ?>
           </div>
         </td>

sections/user/take_edit.php

     }
   }
 }
+
+//2FA deactivation
+if (isset($_POST['disable2fa'])) {
+  $DB->query("
+    SELECT PassHash
+    FROM users_main
+    WHERE ID = $UserID");
+  list($PassHash) = $DB->next_record();
+  if (!Users::check_password($_POST['cur_pass'], $PassHash)) {
+      error('You did not enter the correct password.');
+      header("Location: user.php?action=edit&userid=$UserID");
+      die();
+  }
+  $DB->query("
+    UPDATE users_main
+    SET TwoFactor=NULL
+    WHERE ID = $UserID");
+}
 //End 2FA
 
 if (!$Err && ($_POST['cur_pass'] || $_POST['new_pass_1'] || $_POST['new_pass_2'])) {