How to customize the wp-signup.php for a multisite network?

Question

I googled about customizing wp-signup.php but found no luck. Here's what I need:

1. User will register.
2. During registration process, user will pay first (like paypal or credit card).
3. Create subdomain when user successfully paid.

My problem is: How can I add a payment field in wp-signup.php? I am really new to wordpress. Any guide or link is a big help to me.

Registration form something like this:

• username
• email address
• gimme a site
• payment
• …
• register button

Answer 1

The register form have different hooks for custom fields.

I hope this source example help you.

    /**
     * Add custom field to registration form
     */
    add_action( 'register_form', 'fb_show_first_name_field' );
    add_action( 'register_post', 'fb_check_fields', 10, 3 );
    add_action( 'user_register', 'fb_register_extra_fields' );

    function fb_show_first_name_field() {
    ?>
        <p>
            <label>Twitter<br/>
                <input id="twitter" type="text" tabindex="30" size="25" value="<?php echo $_POST['twitter']; ?>" name="twitter" />
            </label>
        </p>
    <?php
    }

    function fb_check_fields ( $login, $email, $errors ) {
        global $twitter;

        if ( '' === $_POST['twitter'] )
            $errors->add( 'empty_realname', "<strong>ERROR</strong>: Please Enter your twitter handle" );
        else
            $twitter = $_POST['twitter'];

    }

    function fb_register_extra_fields ( $user_id, $password = "", $meta = array() ) {

        update_user_meta( $user_id, 'twitter', $_POST['twitter'] );
    }

It is also usefull, I think, that you add the fields to the rpofile page for changes and view of the field content.

    /**
     * Add additional custom field
     */
    add_action( 'show_user_profile', 'fb_show_extra_profile_fields' );
    add_action( 'edit_user_profile', 'fb_show_extra_profile_fields' );

    function fb_show_extra_profile_fields( $user ) {
    ?>
        <h3>Extra profile information</h3>
        <table class="form-table">
            <tr>
                <th><label for="twitter">Twitter</label></th>
                <td>
                    <input type="text" name="twitter" id="twitter" value="<?php echo esc_attr( get_the_author_meta( 'twitter', $user->ID ) ); ?>" class="regular-text" /><br />
                    <span class="description">Please enter your Twitter username.</span>
                </td>
            </tr>
        </table>
    <?php
    }

    add_action( 'personal_options_update',  'fb_save_extra_profile_fields' );
    add_action( 'edit_user_profile_update', 'fb_save_extra_profile_fields' );
    function fb_save_extra_profile_fields( $user_id ) {

        if ( ! current_user_can( 'edit_user', $user_id ) )
            return FALSE;

        /* Copy and paste this line for additional fields. Make sure to change 'twitter' to the field ID. */
        update_user_meta( $user_id, 'twitter', $_POST['twitter'] );
    }