I am on process of creating a Visa checkout plugin but stuck in generating token

Here are the token requirment:

Format: Alphanumeric; maximum 100 characters in the form of token: x:UNIX_UTC_Timestamp:SHA256_hash, where

UNIX_UTC_Timestamp is a UNIX Epoch timestamp

SHA256_hash is an SHA256 hash of the following unseparated items:

Your shared secret Timestamp from the transaction; exactly the same as UNIX_UTC_Timestamp Resource path (API name). This HTTPS request's query string

Note: The query string includes one or more parameters in name-value pair format, whose names are separated from values by equal signs (=); an empty value may be omitted but the name and equal sign must be present. The initial question mark (?) is not included.

Note: All parameters must be present. The parameters must be in lexicographic sort order (UTF-8, uppercase hex characters) with parameters separated from each other by an ampersand (&).

Note: The query string must be URL encoded (excepting the following characters, per RFC 3986: hyp

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