plaintext property
http://tools.ietf.org/html/rfc5849#section-3.4.3 TODO: Implement RSA-SHA1 http://tools.ietf.org/html/rfc5849#section-3.4.4
Implementation
/// http://tools.ietf.org/html/rfc5849#section-3.4.4
static final SignatureMethod plaintext =
SignatureMethod('PLAINTEXT', (String key, String text) {
return key;
});