Implement Single Logout Protocol

[gonzomir]

This fixes #5. Thoe workflow is are as follows:

1. The user logs out from Wordpress.
   1. After the user has been signed out the plugin send logout request to IdP's SLS.
   2. The IdP logs out the user and sends logout response to sso/sls endpoint.
   3. After processing the response the plugin redirects the user to the original redirect URL or /wp-admin
2. The user logs out from IdP or another SP.
   1. The IdP sends logout request to sso/sls endpoint with a redirect.
   2. The plugin signs out the user and sends logout response to IdP with redirect.

[spacedmonkey]

@shadyvb Any chance of merging this?

[shadyvb]

LGTM, need to do some testing this week before merging.

Thanks @spacedmonkey !

[spacedmonkey]

Any chance this can get merged? @shadyvb

[spacedmonkey]

Updated PR to stop fatal error.

[spacedmonkey]

In Skyscanner#7 it makes the settings more filter so SLS can be filtered to pass other params to wpsimplesaml_idp_metadata filter.

In Skyscanner#6 I fixed the error message.

[tlaverdure]

Hey there, was wondering if there were any plans to get this merged soon? Need this to fulfill a high priority security requirement. Thanks!

[stedaniels]

@shadyvb what needs to be done to get this merged? Anything I can help out on?

[roborourke]

This doesn't guarantee $settings['sp'] is set any more.

Suggested change

	$settings['sp']['entityId'] = $sp_home_url;
	if ( ! isset( $settings['sp'] ) {
	$settings['sp'] = [];
	}
	$settings['sp']['entityId'] = $sp_home_url;