How to change NameID in SimpleSAMLphp

I’m developing a SSO using simpleSAMLphp.

I configured correctly the service provider and the IdP, but I have to send the XML to the SP with a NameID in a specific format.

How can I perform this? In the metadata? or can I do it through the code?

Thanks,

Answer

I sorted already, I post the solution below:

In the IdP authsources config file:

'idp-name' => array(
...
'message' => 'key1:'.$value1.';key2:'.$value2,
...
),

And in the metadata of the Service Provider (saml20-sp-remote.php):

...
'NameIDFormat' => 'urn:oasis:names:tc:SAML:1.1:nameid-format:persistent',
'simplesaml.nameidattribute' => 'message',
...

Then in your code you only have to specify $value1 and $value2 before doing the authentication.

Thanks to Anthony for the help.