Railo 4.2 Reference
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Function HMAC

Creates Hash-based Message Authentication Code for the given string based on the algorithm and encoding.
      Hash-based Message Authentication Code (HMAC) is used to verify the data integrity and authenticity of a messagetransmitted.
      It involves a cryptographic hash function in combination with a secret key.
      The cryptographic hashfunction can be Message Digest 5 (MD5), Secure Hash Algorithm (SHA), and so on


hmac(object message,object key,[string algorithm,[string encoding]]):string


The arguments for this function are set. You can not use other arguments except the following ones.
Name Type Required Description
message object  Yes The message to transmit. The message can be a String or a byte array.  
key object  Yes The secret key to create HMAC. The key can be a String or a byte array.  
algorithm string  No the algorithm used, default is "HmacMD5"  
encoding string  No the encoding used, default encoding is the web charset of the enviroment.