AI 0021 Clarify base64 encoding in POST profile

[Scott Cantor <cantor.2@osu.edu>]

In response to the bit of confusion over character encoding issues in the POST profile, I suggest the following clarifications. Line
numbers are from 1.0 B&P.

On line 692, replace the current sentence with this text:

The notation B64(<response>) stands for the result of applying the Base64 Content-Transfer-Encoding to the response, as defined by
RFC 1521, section 5.2, and SHOULD consist of lines of encoded data of up to 76 characters. The first encoded line begins after the
opening quote signifying the "value" attribute of the SAMLResponse form element.

The character set used to represent the encoded data is determined by the "charset" attribute of the Content-Type of the HTML
document containing the form. The character set of the XML document resulting from decoding the data is determined in the normal
fashion, and defaults to UTF-8 if no character set is indicated.

-- Scott