request_filesystem_credentials( string $form_post, string $type = '', bool $error = false, string $context = '', array $extra_fields = null, bool $allow_relaxed_file_ownership = false )

function request_filesystem_credentials( $form_post, $type = '', $error = false, $context = '', $extra_fields = null, $allow_relaxed_file_ownership = false ) {
	global $pagenow;

	/**
	 * Filters the filesystem credentials form output.
	 *
	 * Returning anything other than an empty string will effectively short-circuit
	 * output of the filesystem credentials form, returning that value instead.
	 *
	 * @since WP-2.5.0
	 * @since WP-4.6.0 The `$context` parameter default changed from `false` to an empty string.
	 *
	 * @param mixed  $output                       Form output to return instead. Default empty.
	 * @param string $form_post                    The URL to post the form to.
	 * @param string $type                         Chosen type of filesystem.
	 * @param bool   $error                        Whether the current request has failed to connect.
	 *                                             Default false.
	 * @param string $context                      Full path to the directory that is tested for
	 *                                             being writable.
	 * @param bool   $allow_relaxed_file_ownership Whether to allow Group/World writable.
	 *                                             Default false.
	 * @param array  $extra_fields                 Extra POST fields.
	 */
	$req_cred = apply_filters( 'request_filesystem_credentials', '', $form_post, $type, $error, $context, $extra_fields, $allow_relaxed_file_ownership );
	if ( '' !== $req_cred )
		return $req_cred;

	if ( empty($type) ) {
		$type = get_filesystem_method( array(), $context, $allow_relaxed_file_ownership );
	}

	if ( 'direct' == $type )
		return true;

	if ( is_null( $extra_fields ) )
		$extra_fields = array( 'version', 'locale' );

	$credentials = get_option('ftp_credentials', array( 'hostname' => '', 'username' => ''));

	$submitted_form = wp_unslash( $_POST );

	// Verify nonce, or unset submitted form field values on failure
	if ( ! isset( $_POST['_fs_nonce'] ) || ! wp_verify_nonce( $_POST['_fs_nonce'], 'filesystem-credentials' ) ) {
		unset(
			$submitted_form['hostname'],
			$submitted_form['username'],
			$submitted_form['password'],
			$submitted_form['public_key'],
			$submitted_form['private_key'],
			$submitted_form['connection_type']
		);
	}

	// If defined, set it to that, Else, If POST'd, set it to that, If not, Set it to whatever it previously was(saved details in option)
	$credentials['hostname'] = defined('FTP_HOST') ? FTP_HOST : (!empty($submitted_form['hostname']) ? $submitted_form['hostname'] : $credentials['hostname']);
	$credentials['username'] = defined('FTP_USER') ? FTP_USER : (!empty($submitted_form['username']) ? $submitted_form['username'] : $credentials['username']);
	$credentials['password'] = defined('FTP_PASS') ? FTP_PASS : (!empty($submitted_form['password']) ? $submitted_form['password'] : '');

	// Check to see if we are setting the public/private keys for ssh
	$credentials['public_key'] = defined('FTP_PUBKEY') ? FTP_PUBKEY : (!empty($submitted_form['public_key']) ? $submitted_form['public_key'] : '');
	$credentials['private_key'] = defined('FTP_PRIKEY') ? FTP_PRIKEY : (!empty($submitted_form['private_key']) ? $submitted_form['private_key'] : '');

	// Sanitize the hostname, Some people might pass in odd-data:
	$credentials['hostname'] = preg_replace('|\w+://|', '', $credentials['hostname']); //Strip any schemes off

	if ( strpos($credentials['hostname'], ':') ) {
		list( $credentials['hostname'], $credentials['port'] ) = explode(':', $credentials['hostname'], 2);
		if ( ! is_numeric($credentials['port']) )
			unset($credentials['port']);
	} else {
		unset($credentials['port']);
	}

	if ( ( defined( 'FTP_SSH' ) && FTP_SSH ) || ( defined( 'FS_METHOD' ) && 'ssh2' == FS_METHOD ) ) {
		$credentials['connection_type'] = 'ssh';
	} elseif ( ( defined( 'FTP_SSL' ) && FTP_SSL ) && 'ftpext' == $type ) { //Only the FTP Extension understands SSL
		$credentials['connection_type'] = 'ftps';
	} elseif ( ! empty( $submitted_form['connection_type'] ) ) {
		$credentials['connection_type'] = $submitted_form['connection_type'];
	} elseif ( ! isset( $credentials['connection_type'] ) ) { //All else fails (And it's not defaulted to something else saved), Default to FTP
		$credentials['connection_type'] = 'ftp';
	}
	if ( ! $error &&
			(
				( !empty($credentials['password']) && !empty($credentials['username']) && !empty($credentials['hostname']) ) ||
				( 'ssh' == $credentials['connection_type'] && !empty($credentials['public_key']) && !empty($credentials['private_key']) )
			) ) {
		$stored_credentials = $credentials;
		if ( !empty($stored_credentials['port']) ) //save port as part of hostname to simplify above code.
			$stored_credentials['hostname'] .= ':' . $stored_credentials['port'];

		unset($stored_credentials['password'], $stored_credentials['port'], $stored_credentials['private_key'], $stored_credentials['public_key']);
		if ( ! wp_installing() ) {
			update_option( 'ftp_credentials', $stored_credentials );
		}
		return $credentials;
	}
	$hostname = isset( $credentials['hostname'] ) ? $credentials['hostname'] : '';
	$username = isset( $credentials['username'] ) ? $credentials['username'] : '';
	$public_key = isset( $credentials['public_key'] ) ? $credentials['public_key'] : '';
	$private_key = isset( $credentials['private_key'] ) ? $credentials['private_key'] : '';
	$port = isset( $credentials['port'] ) ? $credentials['port'] : '';
	$connection_type = isset( $credentials['connection_type'] ) ? $credentials['connection_type'] : '';

	if ( $error ) {
		$error_string = __('<strong>ERROR:</strong> There was an error connecting to the server, Please verify the settings are correct.');
		if ( is_wp_error($error) )
			$error_string = esc_html( $error->get_error_message() );
		echo '<div id="message" class="error"><p>' . $error_string . '</p></div>';
	}

	$types = array();
	if ( extension_loaded('ftp') || extension_loaded('sockets') || function_exists('fsockopen') )
		$types[ 'ftp' ] = __('FTP');
	if ( extension_loaded('ftp') ) //Only this supports FTPS
		$types[ 'ftps' ] = __('FTPS (SSL)');
	if ( extension_loaded('ssh2') && function_exists('stream_get_contents') )
		$types[ 'ssh' ] = __('SSH2');

	/**
	 * Filters the connection types to output to the filesystem credentials form.
	 *
	 * @since WP-2.9.0
	 * @since WP-4.6.0 The `$context` parameter default changed from `false` to an empty string.
	 *
	 * @param array  $types       Types of connections.
	 * @param array  $credentials Credentials to connect with.
	 * @param string $type        Chosen filesystem method.
	 * @param object $error       Error object.
	 * @param string $context     Full path to the directory that is tested
	 *                            for being writable.
	 */
	$types = apply_filters( 'fs_ftp_connection_types', $types, $credentials, $type, $error, $context );

?>
<form action="<?php echo esc_url( $form_post ) ?>" method="post">
<div id="request-filesystem-credentials-form" class="request-filesystem-credentials-form">
<?php
// Print a H1 heading in the FTP credentials modal dialog, default is a H2.
$heading_tag = 'h2';
if ( 'plugins.php' === $pagenow || 'plugin-install.php' === $pagenow ) {
	$heading_tag = 'h1';
}
echo "<$heading_tag id='request-filesystem-credentials-title'>" . __( 'Connection Information' ) . "</$heading_tag>";
?>
<p id="request-filesystem-credentials-desc"><?php
	$label_user = __('Username');
	$label_pass = __('Password');
	_e('To perform the requested action, ClassicPress needs to access your web server.');
	echo ' ';
	if ( ( isset( $types['ftp'] ) || isset( $types['ftps'] ) ) ) {
		if ( isset( $types['ssh'] ) ) {
			_e('Please enter your FTP or SSH credentials to proceed.');
			$label_user = __('FTP/SSH Username');
			$label_pass = __('FTP/SSH Password');
		} else {
			_e('Please enter your FTP credentials to proceed.');
			$label_user = __('FTP Username');
			$label_pass = __('FTP Password');
		}
		echo ' ';
	}
	_e('If you do not remember your credentials, you should contact your web host.');
?></p>
<label for="hostname">
	<span class="field-title"><?php _e( 'Hostname' ) ?></span>
	<input name="hostname" type="text" id="hostname" aria-describedby="request-filesystem-credentials-desc" class="code" placeholder="<?php esc_attr_e( 'example: www.wordpress.org' ) ?>" value="<?php echo esc_attr($hostname); if ( !empty($port) ) echo ":$port"; ?>"<?php disabled( defined('FTP_HOST') ); ?> />
</label>
<div class="ftp-username">
	<label for="username">
		<span class="field-title"><?php echo $label_user; ?></span>
		<input name="username" type="text" id="username" value="<?php echo esc_attr($username) ?>"<?php disabled( defined('FTP_USER') ); ?> />
	</label>
</div>
<div class="ftp-password">
	<label for="password">
		<span class="field-title"><?php echo $label_pass; ?></span>
		<input name="password" type="password" id="password" value="<?php if ( defined('FTP_PASS') ) echo '*****'; ?>"<?php disabled( defined('FTP_PASS') ); ?> />
		<em><?php if ( ! defined('FTP_PASS') ) _e( 'This password will not be stored on the server.' ); ?></em>
	</label>
</div>
<fieldset>
<legend><?php _e( 'Connection Type' ); ?></legend>
<?php
	$disabled = disabled( ( defined( 'FTP_SSL' ) && FTP_SSL ) || ( defined( 'FTP_SSH' ) && FTP_SSH ), true, false );
	foreach ( $types as $name => $text ) : ?>
	<label for="<?php echo esc_attr( $name ) ?>">
		<input type="radio" name="connection_type" id="<?php echo esc_attr( $name ) ?>" value="<?php echo esc_attr( $name ) ?>"<?php checked( $name, $connection_type ); echo $disabled; ?> />
		<?php echo $text; ?>
	</label>
<?php
	endforeach;
?>
</fieldset>
<?php
if ( isset( $types['ssh'] ) ) {
	$hidden_class = '';
	if ( 'ssh' != $connection_type || empty( $connection_type ) ) {
		$hidden_class = ' class="hidden"';
	}
?>
<fieldset id="ssh-keys"<?php echo $hidden_class; ?>>
<legend><?php _e( 'Authentication Keys' ); ?></legend>
<label for="public_key">
	<span class="field-title"><?php _e('Public Key:') ?></span>
	<input name="public_key" type="text" id="public_key" aria-describedby="auth-keys-desc" value="<?php echo esc_attr($public_key) ?>"<?php disabled( defined('FTP_PUBKEY') ); ?> />
</label>
<label for="private_key">
	<span class="field-title"><?php _e('Private Key:') ?></span>
	<input name="private_key" type="text" id="private_key" value="<?php echo esc_attr($private_key) ?>"<?php disabled( defined('FTP_PRIKEY') ); ?> />
</label>
<p id="auth-keys-desc"><?php _e( 'Enter the location on the server where the public and private keys are located. If a passphrase is needed, enter that in the password field above.' ) ?></p>
</fieldset>
<?php
}

foreach ( (array) $extra_fields as $field ) {
	if ( isset( $submitted_form[ $field ] ) )
		echo '<input type="hidden" name="' . esc_attr( $field ) . '" value="' . esc_attr( $submitted_form[ $field ] ) . '" />';
}
?>
	<p class="request-filesystem-credentials-action-buttons">
		<?php wp_nonce_field( 'filesystem-credentials', '_fs_nonce', false, true ); ?>
		<button class="button cancel-button" data-js-action="close" type="button"><?php _e( 'Cancel' ); ?></button>
		<?php submit_button( __( 'Proceed' ), '', 'upgrade', false ); ?>
	</p>
</div>
</form>
<?php
	return false;
}