<script src='https://www.google.com/recaptcha/api.js'></script>
<button
class="g-recaptcha"
data-sitekey="6LfgNmAUAAAAAFEQ1jDvPhkICQs8UgJSqvgj1-8-"
data-callback="YourOnSubmitFn">
Submit
</button>

<form method="post" id="login" autocomplete="false">

<input type="text" name="username" placeholder="Email" value="" required />

<input type="password" name="password" placeholder="Password" minlength="" maxlength="25" required />

<input class="button" name="submit" type="submit" value="Sign in"/>

</form>