!!! Overview
[{$pagename}] is the [OAuth state parameter] hash value and is the [base64url] encoding of the left-most half of the [hash] of the octets of the [ASCII] representation of the state value, where the [hash] algorithm used is [id_token]'s [alg] [JOSE Header Parameter] Header. 

[{$pagename}] value is a [Case-sensitive] [string].

For [example], if the alg is [HS512], [hash] the code value with [SHA-512], then take the left-most 256 [bits] and [base64url] encode them. 

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]