Description:
------------
base64_decode handles a pad as the end of data even when it is not 
terminating a string, in which case it really should be handled as non-
alphabet characters. From rfc 3548 2.3: "Furthermore, such 
specifications may consider the pad character, "=", as not part of the 
base alphabet until the end of the string."

By ignoring all data after the pad, it is difficult to work with 
signature based technologies where the base64 
decoded octects must be compared to determine validity. PHP allows for 
additional data to be added to a signature which ends up being ignored 
when compared, while other implementations do not.

Reproduce code:
---------------
if (base64_decode("dGVzdA==") == base64_decode("dGVzdA==CRAP")) {
    echo "Same octect data - Signature Valid";
} else {
    echo "Invalid Signature";
}

Expected result:
----------------
Invalid Signature

Actual result:
--------------
Same octect data - Signature Valid