How to validate Google reCAPTCHA v3 on server side?

Php Problem Overview

I've just set up the new google recaptcha with checkbox, it's working fine on front end, however I don't know how to handle it on server side using PHP. I've tried to use the old code below but the form is sent even if the captcha is not valid.

require_once('recaptchalib.php');
$privatekey = "my key";
$resp = recaptcha_check_answer ($privatekey,
        $_SERVER["REMOTE_ADDR"],
        $_POST["recaptcha_challenge_field"],
        $_POST["recaptcha_response_field"]);

if (!$resp->is_valid) {
 $errCapt='<p style="color:#D6012C ">The CAPTCHA Code wasnot entered correctly.</p>';}

Php Solutions

Solution 1 - Php

Private key safety

While the answers here are definately working, they are using a GET request, which exposes your private key (even though https is used). On Google Developers the specified method is POST.

For a little bit more detail: https://stackoverflow.com/a/323286/1680919

Verification via POST

function isValid() 
{
    try {

        $url = 'https://www.google.com/recaptcha/api/siteverify';
        $data = ['secret'   => '[YOUR SECRET KEY]',
                 'response' => $_POST['g-recaptcha-response'],
                 'remoteip' => $_SERVER['REMOTE_ADDR']];
                 
        $options = [
            'http' => [
                'header'  => "Content-type: application/x-www-form-urlencoded\r\n",
                'method'  => 'POST',
                'content' => http_build_query($data) 
            ]
        ];
    
        $context  = stream_context_create($options);
        $result = file_get_contents($url, false, $context);
        return json_decode($result)->success;
    }
    catch (Exception $e) {
        return null;
    }
}

Array Syntax: I use the "new" array syntax ( [ and ] instead of array(..) ). If your php version does not support this yet, you will have to edit those 3 array definitions accordingly (see comment).

Return Values: This function returns true if the user is valid, false if not, and null if an error occured. You can use it for example simply by writing if (isValid()) { ... }

Solution 2 - Php

this is solution

index.html

<html>
  <head>
    <title>Google recapcha demo - Codeforgeek</title>
    <script src='https://www.google.com/recaptcha/api.js'></script>
  </head>
  <body>
    <h1>Google reCAPTHA Demo</h1>
    <form id="comment_form" action="form.php" method="post">
      <input type="email" placeholder="Type your email" size="40"><br><br>
      <textarea name="comment" rows="8" cols="39"></textarea><br><br>
      <input type="submit" name="submit" value="Post comment"><br><br>
      <div class="g-recaptcha" data-sitekey="=== Your site key ==="></div>
    </form>
  </body>
</html>

verify.php

<?php
    $email; $comment; $captcha;

    if(isset($_POST['email']))
        $email=$_POST['email'];
    if(isset($_POST['comment']))
        $comment=$_POST['comment'];
    if(isset($_POST['g-recaptcha-response']))
        $captcha=$_POST['g-recaptcha-response'];
        
    if(!$captcha){
        echo '<h2>Please check the the captcha form.</h2>';
        exit;
    }

    $response = json_decode(file_get_contents("https://www.google.com/recaptcha/api/siteverify?secret=YOUR SECRET KEY&response=".$captcha."&remoteip=".$_SERVER['REMOTE_ADDR']), true);
    if($response['success'] == false)
    {
        echo '<h2>You are spammer ! Get the @$%K out</h2>';
    }
    else
    {
        echo '<h2>Thanks for posting comment.</h2>';
    }
?>

http://codeforgeek.com/2014/12/google-recaptcha-tutorial/

Solution 3 - Php

I'm not a fan of any of these solutions. I use this instead:

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://www.google.com/recaptcha/api/siteverify");
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); 
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, [
	'secret' => $privatekey,
	'response' => $_POST['g-recaptcha-response'],
	'remoteip' => $_SERVER['REMOTE_ADDR']
]);

$resp = json_decode(curl_exec($ch));
curl_close($ch);

if ($resp->success) {
    // Success
} else {
    // failure
}

I'd argue that this is superior because you ensure it is being POSTed to the server and it's not making an awkward 'file_get_contents' call. This is compatible with recaptcha 2.0 described here: https://developers.google.com/recaptcha/docs/verify

I find this cleaner. I see most solutions are file_get_contents, when I feel curl would suffice.

Solution 4 - Php

Easy and best solution is the following.
index.html

<form action="submit.php" method="POST">
   <input type="text" name="name" value="" />
   <input type="text" name="email" value="" />
   <textarea type="text" name="message"></textarea>
   <div class="g-recaptcha" data-sitekey="Insert Your Site Key"></div>
   <input type="submit" name="submit" value="SUBMIT">
</form>

submit.php

<?php
if(isset($_POST['submit']) && !empty($_POST['submit'])){
  if(isset($_POST['g-recaptcha-response']) && !empty($_POST['g-recaptcha-response'])){
    //your site secret key
    $secret = 'InsertSiteSecretKey';
    //get verify response data
    $verifyResponse = file_get_contents('https://www.google.com/recaptcha/api/siteverify?secret='.$secret.'&response='.$_POST['g-recaptcha-response']);
    $responseData = json_decode($verifyResponse);
    if($responseData->success){
        //contact form submission code goes here
        
        $succMsg = 'Your contact request have submitted successfully.';
    }else{
        $errMsg = 'Robot verification failed, please try again.';
    }
  }else{
    $errMsg = 'Please click on the reCAPTCHA box.';
  }
}
?>

I have found this reference and full tutorial from here - Using new Google reCAPTCHA with PHP

Solution 5 - Php

I liked Levit's answer and ended up using it. But I just wanted to point out, just in case, that there is an official Google PHP library for new reCAPTCHA: https://github.com/google/recaptcha

The latest version (right now 1.1.2) supports Composer and contains an example that you can run to see if you have configured everything correctly.

Below you can see part of the example that comes with this official library (with my minor modifications for clarity):

// Make the call to verify the response and also pass the user's IP address
    $resp = $recaptcha->verify($_POST['g-recaptcha-response'], $_SERVER['REMOTE_ADDR']);

    if ($resp->isSuccess()) {
// If the response is a success, that's it!
        ?>
        <h2>Success!</h2>
        <p>That's it. Everything is working. Go integrate this into your real project.</p>
        <p><a href="/">Try again</a></p>
        <?php
    } else {
// If it's not successful, then one or more error codes will be returned.
        ?>
        <h2>Something went wrong</h2>
        <p>The following error was returned: <?php
            foreach ($resp->getErrorCodes() as $code) {
                echo '<tt>' , $code , '</tt> ';
            }
            ?></p>
        <p>Check the error code reference at <tt><a href="https://developers.google.com/recaptcha/docs/verify#error-code-reference">https://developers.google.com/recaptcha/docs/verify#error-code-reference</a></tt>.
        <p><strong>Note:</strong> Error code <tt>missing-input-response</tt> may mean the user just didn't complete the reCAPTCHA.</p>
        <p><a href="/">Try again</a></p>
    <?php
    }

Hope it helps someone.

Solution 6 - Php

In the example above. For me, this if($response.success==false) thing does not work. Here is correct PHP code:

$url = 'https://www.google.com/recaptcha/api/siteverify';
$privatekey = "--your_key--";
$response = file_get_contents($url."?secret=".$privatekey."&response=".$_POST['g-recaptcha-response']."&remoteip=".$_SERVER['REMOTE_ADDR']);
$data = json_decode($response);
    				
if (isset($data->success) AND $data->success==true) {
    		// everything is ok!
} else {
            // spam
}

Solution 7 - Php

To verify at server side using PHP. Two most important thing you need to consider.

1. $_POST['g-recaptcha-response']

2.$secretKey = '6LeycSQTAAAAAMM3AeG62pBslQZwBTwCbzeKt06V';

$verifydata = file_get_contents('https://www.google.com/recaptcha/api/siteverify?secret='.$secretKey.'&response='.$_POST['g-recaptcha-response']);
        $response= json_decode($verifydata);

If you get $verifydata true, You done.
For more check out this
Google reCaptcha Using PHP | Only 2 Step Integration

Solution 8 - Php

it is similar with mattgen88, but I just fixed CURLOPT_HEADER, and redefine array for it work in domain.com host server. this one doesn't work on my xampp localhost. Those small error but took long to figure out. this code was tested on domain.com hosting.

   $privatekey = 'your google captcha private key';
 
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, "https://www.google.com/recaptcha/api/siteverify");
    curl_setopt($ch, CURLOPT_HEADER, 'Content-Type: application/json');
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); 
    curl_setopt($ch, CURLOPT_POST, 1);
    curl_setopt($ch, CURLOPT_POSTFIELDS, array(
        'secret' => $privatekey,
        'response' => $_POST['g-recaptcha-response'],
        'remoteip' => $_SERVER['REMOTE_ADDR']
    )
               );

    $resp = json_decode(curl_exec($ch));
    curl_close($ch);

    if ($resp->success) {
        // Success
        echo 'captcha';
    } else {
        // failure
        echo 'no captcha';
    }

Solution 9 - Php

Here you have simple example. Just remember to provide secretKey and siteKey from google api.

<?php
$siteKey = 'Provide element from google';
$secretKey = 'Provide element from google';

if($_POST['submit']){
    $username = $_POST['username'];
    $responseKey = $_POST['g-recaptcha-response'];
    $userIP = $_SERVER['REMOTE_ADDR'];
    $url = "https://www.google.com/recaptcha/api/siteverify?secret=$secretKey&response=$responseKey&remoteip=$userIP";
    $response = file_get_contents($url);
    $response = json_decode($response);
    if($response->success){
        echo "Verification is correct. Your name is $username";
    } else {
        echo "Verification failed";
    }
} ?>

<html>
<meta>
    <title>Google ReCaptcha</title>
</meta>
<body>
    <form action="index.php" method="post">
        <input type="text" name="username" placeholder="Write your name"/>
        <div class="g-recaptcha" data-sitekey="<?= $siteKey ?>"></div>
        <input type="submit" name="submit" value="send"/>
    </form>
    <script src='https://www.google.com/recaptcha/api.js'></script>
</body>

Solution 10 - Php

Source Tutorial Link

V2 of Google reCAPTCHA.

Step 1 - Go to Google reCAPTCHA

Step 2 - Download PHP code here and upload src folder on your server.

Step 3 - Use below code in your form.php

		<head>
		    <title>FreakyJolly.com Google reCAPTCHA EXAMPLE form</title>
		    <script src='https://www.google.com/recaptcha/api.js'></script>
		</head>

		<body>
		    <?php

			require('src/autoload.php');

			$siteKey = '6LegPmIUAAAAADLwDmXXXXXXXyZAJVJXXXjN';
			$secret = '6LegPmIUAAAAAO3ZTXXXXXXXXJwQ66ngJ7AlP';

			$recaptcha = new \ReCaptcha\ReCaptcha($secret);

			$gRecaptchaResponse = $_POST['g-recaptcha-response']; //google captcha post data
			$remoteIp = $_SERVER['REMOTE_ADDR']; //to get user's ip

			$recaptchaErrors = ''; // blank varible to store error

			$resp = $recaptcha->verify($gRecaptchaResponse, $remoteIp); //method to verify captcha
			if ($resp->isSuccess()) {

			   /******** 
			   
				Add code to create User here when form submission is successful
			   
			   *****/
			   
			} else {
				
				/****
				
				// This variable will have error when reCAPTCHA is not entered correctly.
				
				****/

			   $recaptchaErrors = $resp->getErrorCodes(); 
			}


			?>
		        <form autcomplete="off" class="form-createuser" name="create_user_form" action="" method="post">
		            <div class="panel periodic-login">
		                <div class="panel-body text-center">
		                    <div class="form-group form-animate-text" style="margin-top:40px !important;">
		                        <input type="text" autcomplete="off" class="form-text" name="new_user_name" required="">
		                        <span class="bar"></span>
		                        <label>Username</label>
		                    </div>
		                    <div class="form-group form-animate-text" style="margin-top:40px !important;">
		                        <input type="text" autcomplete="off" class="form-text" name="new_phone_number" required="">
		                        <span class="bar"></span>
		                        <label>Phone</label>
		                    </div>
		                    <div class="form-group form-animate-text" style="margin-top:40px !important;">
		                        <input type="password" autcomplete="off" class="form-text" name="new_user_password" required="">
		                        <span class="bar"></span>
		                        <label>Password</label>
		                    </div>
		                    <?php 
									if(isset($recaptchaErrors[0])){
										print('Error in Submitting Form. Please Enter reCAPTCHA AGAIN');
									}
							  ?>
		                    <div class="g-recaptcha" data-sitekey="6LegPmIUAAAAADLwDmmVmXXXXXXXXXXXXXXjN"></div>
		                    <input type="submit" class="btn col-md-12" value="Create User">
		                </div>
		            </div>
		        </form>
		</body>

		</html>

Solution 11 - Php

In response to @mattgen88's answer ,Here is a CURL method with better arrangement:

   //$secret= 'your google captcha private key';
	$curl = curl_init();
	curl_setopt_array($curl, array(
		CURLOPT_URL 			=> "https://www.google.com/recaptcha/api/siteverify",
		CURLOPT_HEADER			=> "Content-Type: application/json",
		CURLOPT_RETURNTRANSFER 	=> true,
		CURLOPT_SSL_VERIFYPEER 	=> FALSE, // to disable ssl verifiction set to false else true
		//CURLOPT_ENCODING 		=> "",
		CURLOPT_MAXREDIRS 		=> 10,
		CURLOPT_TIMEOUT 		=> 30,
		CURLOPT_HTTP_VERSION 	=> CURL_HTTP_VERSION_1_1,
		CURLOPT_CUSTOMREQUEST 	=> "POST",
		CURLOPT_POSTFIELDS 		=> array(
			'secret' => $secret,
			'response' => $_POST['g-recaptcha-response'],
			'remoteip' => $_SERVER['REMOTE_ADDR']
		)
	));

	$response = json_decode(curl_exec($curl));
	$err = curl_error($curl);

	curl_close($curl);

	if ($response->success) {
		echo 'captcha';
	} 
	else if ($err){
		echo $err;
	}	
	else {
		echo 'no captcha';
	}

Solution 12 - Php

Check below example

<script src='https://www.google.com/recaptcha/api.js'></script>
<script>

function get_action(form) 
{
    var v = grecaptcha.getResponse();
    if(v.length == 0)
    {
        document.getElementById('captcha').innerHTML="You can't leave Captcha Code empty";
        return false;
    }
    else
    {
         document.getElementById('captcha').innerHTML="Captcha completed";
        return true; 
    }
}

</script>
<form autocomplete="off" method="post" action=submit.php">
					
	<input type="text" name="name">
	<input type="text" name="email">
	<div class="g-recaptcha" id="rcaptcha"  data-sitekey="site key"></div>
	<span id="captcha" style="color:red" /></span> <!-- this will show captcha errors -->
	<input type="submit" id="sbtBrn" value="Submit" name="sbt" class="btn btn-info contactBtn" />
</form>

Content Type	Original Author	Original Content on Stackoverflow
Question	Moatez	View Question on Stackoverflow
Solution 1 - Php	Levite	View Answer on Stackoverflow
Solution 2 - Php	SoCix	View Answer on Stackoverflow
Solution 3 - Php	mattgen88	View Answer on Stackoverflow
Solution 4 - Php	JoyGuru	View Answer on Stackoverflow
Solution 5 - Php	Yerke	View Answer on Stackoverflow
Solution 6 - Php	Viktor Kashlyaev	View Answer on Stackoverflow
Solution 7 - Php	Roshan Padole	View Answer on Stackoverflow
Solution 8 - Php	Võ Minh	View Answer on Stackoverflow
Solution 9 - Php	Adam Kozlowski	View Answer on Stackoverflow
Solution 10 - Php	Code Spy	View Answer on Stackoverflow
Solution 11 - Php	MR_AMDEV	View Answer on Stackoverflow
Solution 12 - Php	Pankaj Upadhyay	View Answer on Stackoverflow