Commits on Oct 26, 2022

1. Add SASLprep. Code generated & tested with RFC3454 …

   RFC-4422 recommends that mechanisms SHOULD prepare simple usernames and
   passwords with SASLprep.  And SASLprep is required by the `SCRAM-*`
   mechanisms, which will be added in a future PR.
   
   SASLprep is also recommended for the `PLAIN` SASL mechanism and for the
   `ACL` IMAP extension but—in both cases—string preparation is done by the
   *server*, at its own discretion.
   
   SASLprep has been officially obsoleted by PRECIS.  I don't believe any
   IMAP RFCs have allowed replacing SASLprep with PRECIS yet.  In contrast,
   RFC-7622 updates XMPP to require PRECIS.  (See RFC-8265 for more info on
   PRECIS, and Section 6 for migration considerations.)
   
   Rather than create a fully generic StringPrep superclass or function,
   the SASLprep profile is optimized.  Just enough of the generic
   StringPrep algorithm has been implemented to provide more detailed
   errors for prohibited strings.  Future PRs can expand it as needed, to
   implement other profiles.  In particular, the `trace` StringPrep profile
   is a requirement for clients using the `ANONYMOUS` mechanism.
   
   Many other StringPrep implementations store the tables as an array of
   ranges and loop over every character in the input.  But using Regexp is
   simpler and much faster, especially where the tables closely match
   Unicode character classes (benchmarks are included).  Some StringPrep
   tables use Regexps that are generated from the RFC-3454 appendices.
   Manually written regular expressions are used in cases where there is a
   close match between Unicode character classes and the SASLprep tables.
   All regexps are tested against the RFC tables with every valid
   codepoint, to verify they aren't broken if their character classes are
   changed by new versions of Unicode.
   
   Additionally:
   
   * Added `rake rfcs` to download many IMAP-related RFCs, for convenience.
   * The new code is namespaced under `Net::IMAP::SASL`.  We could move the
     authenticators there too.  If SASL funcionality is ever extracted to
     another gem, we can use: `Net::IMAP::SASL = Net::SASL` for backward
     compatibility.

   

   nevans committed Oct 26, 2022
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