avoid duplicating ldaptor code in LDAPServerWithUPNBind

[graingert]

Contributor Checklist:

• I have updated the release notes at docs/source/NEWS.rst
• I have updated the automated tests.
• All tests pass on your local dev environment. See CONTRIBUTING.rst.

[codecov]

Codecov Report

Merging #161 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #161      +/-   ##
==========================================
- Coverage   93.35%   93.35%   -0.01%     
==========================================
  Files          72       72              
  Lines        9915     9914       -1     
  Branches      973      972       -1     
==========================================
- Hits         9256     9255       -1     
  Misses        537      537              
  Partials      122      122

Impacted Files	Coverage Δ
ldaptor/protocols/ldap/ldapserver.py	80.45% <100%> (-0.07%)	⬇️
ldaptor/test/test_server.py	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7c6f5c3...e42ede9. Read the comment docs.

[adiroiban]

Thanks for the cleanup.
@graingert let us know when you think this is ready for review :)

[graingert]

@adiroiban I think it's ready to go

[adiroiban]

Maybe something like this

Suggested change

	def _request():
	if not (b"@" in request.dn and b"," not in request.dn):
	defer.returnValue(request)
	def _resolveUPNBindDN():
	"""
	See if we have an MS UPN style BIND DN request and resolve it to the
	actual LDAP BindDN.
	UPN bind is in the form of User.Name@ad.example.tld
	"""
	if b"@" not in request.dn or b"," in request.dn:
	# This is not an UPN bind request.
	defer.returnValue(request)

[adiroiban]

Suggested change

	# This might be an UPN request.
	# The the LDAP DN associated with the UPN request.

[adiroiban]

Suggested change

	if len(results) != 1:
	defer.returnValue(request)
	if len(results) != 1:
	# We could not find an exact UPN match so we go with the
	# requested Bind DN.
	defer.returnValue(request)

[adiroiban]

Thanks for the cleanup.

Please see my comments.

Even thou I wrote this code a few months ago, I feel that it needs more documentation.
With the current version, at the first read it was hard to understand what is going on there and why we have all that logic.