UrlEncodedFormat: Encoding space characters - plus (+) vs %20

I came across an issue with UrlEncodedFormat() today - signatures calculated by an CF9-based system always appeared to be invalid and as it seems ColdFusion is ignoring the standards when it comes to encoding of form posts (application/x-www-form-urlencoded).

The document describing the standard on W3 clearly states:

application/x-www-form-urlencoded

This is the default content type. Forms submitted with this content type must be encoded as follows:

1. Control names and values are escaped. Space characters are replaced by `+', and then reserved characters are escaped as described in [RFC1738], section 2.2: Non-alphanumeric characters are replaced by `%HH', a percent sign and two hexadecimal digits representing the ASCII code of the character. Line breaks are represented as "CR LF" pairs (i.e., `%0D%0A').
2. The control names/values are listed in the order they appear in the document. The name is separated from the value by `=' and name/value pairs are separated from each other by `&'.

When you perform an UrlEncodedFormat( ' ' ) on CF, it will return %20, the same call on railo will return "+" as described in the article above.

I solved the issue by simply replacing %20 with +.