[@robin-w Moderator 12 years, 5 months ago]

If you want a quick solution to this

create a directory within your theme called bbpress

ie wp-content/your-theme-name/bbpress

And into this folder copy the following file

bbpress/templates/default/bbpress/form-reply.php

Then alter this file to have a new line 175 as follows

<p> <?php echo do_shortcode ('[bbp-login]') ; ?>

so that

<div id="no-reply-<?php bbp_topic_id(); ?>" class="bbp-no-reply">
		<div class="bbp-template-notice">
			<p><?php is_user_logged_in() ? _e( 'You cannot reply to this topic.', 'bbpress' ) : _e( 'You must be logged in to reply to this topic.', 'bbpress' ); ?></p>
	</div>
	</div>

becomes

<div id="no-reply-<?php bbp_topic_id(); ?>" class="bbp-no-reply">
		<div class="bbp-template-notice">
			<p><?php is_user_logged_in() ? _e( 'You cannot reply to this topic.', 'bbpress' ) : _e( 'You must be logged in to reply to this topic.', 'bbpress' ); ?></p>
		<p> <?php echo do_shortcode ('[bbp-login]') ; ?>
		</div>
	</div>

Save this file, and bbpress will use this and a login panel will be displayed.