In metadata/saml20-sp-remote.php, register your Servider Provider like this:
/* Replace example.com with your atlassian domain name. */
$metadata['https://example.com/plugins/servlet/saml/metadata'] = array(
'AssertionConsumerService' => 'https://example.com/',
'SingleLogoutService' => 'https://example.com/',
'NameIDFormat' => 'urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress',
'simplesaml.nameidattribute' => 'mail',
'simplesaml.attributes' => true,
'attributes' => array('mail', 'givenname', 'sn', 'memberOf'),
);