🔒 Clarify usage of username vs authcid vs authzid

Different SASL mechanisms use the term "username" differently. In
general the pattern seems to be the following:

* Some mechanisms avoid using the term `username` at all, and instead
  use the terms Authentication Identity (`authcid`) and Authorization
  Identity (`authzid`).
* Older or non-standard mechanisms may not distinguish clearly between
  `authcid` and `authzid`. `username` may be semantically equivalent to
  `authcid`, `authzid`, or both.
* When the mechanism supports an explicit `authcid` and an `authzid`,
  `username` commonly refers to the `authcid`.
* When the authentication identity is derived from other credentials,
  `username` commonly refers to the `authzid`.

Every mechanism's keyword arguments, positional arguments, and
documentation is updated to match this terminology.  Aliases have been
added from `username` to `authcid` or `authzid`—or in the other
direction, from `authcid` or `authzd` to `username`.

lib/net/imap/sasl/digest_md5_authenticator.rb

@@ -20,8 +20,9 @@ class Net::IMAP::SASL::DigestMD5Authenticator
   # "Authentication identity" is the generic term used by
   # RFC-4422[https://tools.ietf.org/html/rfc4422].
   # RFC-4616[https://tools.ietf.org/html/rfc4616] and many later RFCs abbreviate
-  # that to +authcid+.  So +authcid+ is available as an alias for #username.
+  # this to +authcid+.
   attr_reader :username
+  alias authcid username
 
   # A password or passphrase that matches the #username.
   #
@@ -44,16 +45,19 @@ class Net::IMAP::SASL::DigestMD5Authenticator
   # :call-seq:
   #   new(username,  password,  authzid = nil, **options) -> authenticator
   #   new(username:, password:, authzid:  nil, **options) -> authenticator
+  #   new(authcid:,  password:, authzid:  nil, **options) -> authenticator
   #
   # Creates an Authenticator for the "+DIGEST-MD5+" SASL mechanism.
   #
   # Called by Net::IMAP#authenticate and similar methods on other clients.
   #
   # ==== Parameters
   #
-  # * #username — Identity whose #password is used.
-  # * #password — A password or passphrase associated with this #username.
+  # * #authcid  ― Authentication identity that is associated with #password.
   #
+  #   #username ― An alias for +authcid+.
+  #
+  # * #password ― A password or passphrase associated with this #authcid.
   #
   # * _optional_ #authzid  ― Authorization identity to act as or on behalf of.
   #
@@ -65,8 +69,10 @@ class Net::IMAP::SASL::DigestMD5Authenticator
   # Any other keyword arguments are silently ignored.
   def initialize(user = nil, pass = nil, authz = nil,
                  username: nil, password: nil, authzid: nil,
+                 authcid: nil,
                  warn_deprecation: true, **)
-    username ||= user or raise ArgumentError, "missing username"
+    username = authcid || username || user or
+      raise ArgumentError, "missing username (authcid)"
     password ||= pass or raise ArgumentError, "missing password"
     authzid  ||= authz
     if warn_deprecation

lib/net/imap/sasl/external_authenticator.rb

@@ -25,9 +25,12 @@ class ExternalAuthenticator
         #     imap.authenticate "PLAIN", "root", passwd, authzid: "user"
         #
         attr_reader :authzid
+        alias username authzid
 
         # :call-seq:
         #   new(authzid: nil, **) -> authenticator
+        #   new(username: nil, **) -> authenticator
+        #   new(username = nil, **) -> authenticator
         #
         # Creates an Authenticator for the "+EXTERNAL+" SASL mechanism, as
         # specified in RFC-4422[https://tools.ietf.org/html/rfc4422].  To use
@@ -38,8 +41,16 @@ class ExternalAuthenticator
         #
         # * _optional_ #authzid  ― Authorization identity to act as or on behalf of.
         #
+        #   _optional_ #username ― An alias for #authzid.
+        #
+        #   Note that, unlike some other authenticators, +username+ sets the
+        #   _authorization_ identity and not the _authentication_ identity.  The
+        #   authentication identity is established for the client by the
+        #   external credentials.
+        #
         # Any other keyword parameters are quietly ignored.
-        def initialize(authzid: nil, **)
+        def initialize(user = nil, authzid: nil, username: nil, **)
+          authzid ||= username || user
           @authzid = authzid&.to_str&.encode "UTF-8"
           if @authzid&.match?(/\u0000/u) # also validates UTF8 encoding
             raise ArgumentError, "contains NULL"

lib/net/imap/sasl/oauthbearer_authenticator.rb

@@ -27,6 +27,7 @@ class OAuthAuthenticator
         #     imap.authenticate "PLAIN", "root", passwd, authzid: "user"
         #
         attr_reader :authzid
+        alias username authzid
 
         # Hostname to which the client connected.  (optional)
         attr_reader :host
@@ -45,6 +46,7 @@ class OAuthAuthenticator
 
         # The query string.  (optional)
         attr_reader :qs
+        alias query qs
 
         # Stores the most recent server "challenge".  When authentication fails,
         # this may hold information about the failure reason, as JSON.
@@ -61,23 +63,34 @@ class OAuthAuthenticator
         # #host or #port) <b>as are specific server implementations</b>.
         #
         # * _optional_ #authzid  ― Authorization identity to act as or on behalf of.
+        #
+        #   _optional_ #username — An alias for #authzid.
+        #
+        #   Note that, unlike some other authenticators, +username+ sets the
+        #   _authorization_ identity and not the _authentication_ identity.  The
+        #   authentication identity is established for the client by the OAuth
+        #   token.
+        #
         # * _optional_ #host — Hostname to which the client connected.
         # * _optional_ #port — Service port to which the client connected.
         # * _optional_ #mthd — HTTP method
         # * _optional_ #path — HTTP path data
         # * _optional_ #post — HTTP post data
         # * _optional_ #qs   — HTTP query string
         #
+        #   _optional_ #query — An alias for #qs
+        #
         # Any other keyword parameters are quietly ignored.
         def initialize(authzid: nil, host: nil, port: nil,
+                       username: nil, query: nil,
                        mthd: nil, path: nil, post: nil, qs: nil, **)
-          @authzid = authzid
+          @authzid = authzid || username
           @host    = host
           @port    = port
           @mthd    = mthd
           @path    = path
           @post    = post
-          @qs      = qs
+          @qs      = qs || query
           @done    = false
         end
 
@@ -144,6 +157,14 @@ class OAuthBearerAuthenticator < OAuthAuthenticator
         # The most common ones are:
         #
         # * _optional_ #authzid  ― Authorization identity to act as or on behalf of.
+        #
+        #   _optional_ #username — An alias for #authzid.
+        #
+        #   Note that, unlike some other authenticators, +username+ sets the
+        #   _authorization_ identity and not the _authentication_ identity.  The
+        #   authentication identity is established for the client by
+        #   #oauth2_token.
+        #
         # * _optional_ #host — Hostname to which the client connected.
         # * _optional_ #port — Service port to which the client connected.
         #

lib/net/imap/sasl/plain_authenticator.rb

@@ -22,6 +22,7 @@ class Net::IMAP::SASL::PlainAuthenticator
   # RFC-4616[https://tools.ietf.org/html/rfc4616] and many later RFCs abbreviate
   # this to +authcid+.
   attr_reader :username
+  alias authcid username
 
   # A password or passphrase that matches the #username.
   attr_reader :password
@@ -42,15 +43,19 @@ class Net::IMAP::SASL::PlainAuthenticator
   # :call-seq:
   #   new(username,  password,  authzid: nil, **) -> authenticator
   #   new(username:, password:, authzid: nil, **) -> authenticator
+  #   new(authcid:,  password:, authzid: nil, **) -> authenticator
   #
   # Creates an Authenticator for the "+PLAIN+" SASL mechanism.
   #
   # Called by Net::IMAP#authenticate and similar methods on other clients.
   #
   # ==== Parameters
   #
-  # * #username ― Identity whose +password+ is used.
-  # * #password ― Password or passphrase associated with this username+.
+  # * #authcid ― Authentication identity that is associated with #password.
+  #
+  #   #username ― An alias for #authcid.
+  #
+  # * #password ― A password or passphrase associated with the #authcid.
   #
   # * _optional_ #authzid  ― Authorization identity to act as or on behalf of.
   #
@@ -59,12 +64,14 @@ class Net::IMAP::SASL::PlainAuthenticator
   #
   # Any other keyword parameters are quietly ignored.
   def initialize(user = nil, pass = nil,
+                 authcid: nil,
                  username: nil, password: nil, authzid: nil, **)
-    [username, user].compact.count == 1 or
-      raise ArgumentError, "conflicting values for username"
-    [password, pass].compact.count == 1 or
+    [authcid, username, user].compact.count <= 1 or
+      raise ArgumentError, "conflicting values for username (authcid)"
+    [password, pass].compact.count <= 1 or
       raise ArgumentError, "conflicting values for password"
-    username ||= user or raise ArgumentError, "missing username"
+    username ||= authcid || user or
+      raise ArgumentError, "missing username (authcid)"
     password ||= pass or raise ArgumentError, "missing password"
     raise ArgumentError, "username contains NULL" if username.include?(NULL)
     raise ArgumentError, "password contains NULL" if password.include?(NULL)

lib/net/imap/sasl/scram_authenticator.rb

@@ -60,6 +60,7 @@ class ScramAuthenticator
         # :call-seq:
         #   new(username,  password,  **options) -> auth_ctx
         #   new(username:, password:, **options) -> auth_ctx
+        #   new(authcid:,  password:, **options) -> auth_ctx
         #
         # Creates an authenticator for one of the "+SCRAM-*+" SASL mechanisms.
         # Each subclass defines #digest to match a specific mechanism.
@@ -68,14 +69,18 @@ class ScramAuthenticator
         #
         # === Parameters
         #
-        # * #username ― Identity whose #password is used.  Aliased as #authcid.
+        # * #authcid  ― Identity whose #password is used.
+        #
+        #   #username - An alias for #authcid.
         # * #password ― Password or passphrase associated with this #username.
         # * _optional_ #authzid ― Alternate identity to act as or on behalf of.
         # * _optional_ #min_iterations - Overrides the default value (4096).
         #
         # Any other keyword parameters are quietly ignored.
         def initialize(username_arg = nil, password_arg = nil,
-                       username: nil, password: nil, authcid: nil, authzid: nil,
+                       authcid: nil, username: nil,
+                       authzid: nil,
+                       password: nil,
                        min_iterations: 4096, # see both RFC5802 and RFC7677
                        cnonce: nil, # must only be set in tests
                        **options)
@@ -92,6 +97,7 @@ def initialize(username_arg = nil, password_arg = nil,
           @min_iterations = Integer min_iterations
           @min_iterations.positive? or
             raise ArgumentError, "min_iterations must be positive"
+
           @cnonce = cnonce || SecureRandom.base64(32)
         end
 

lib/net/imap/sasl/xoauth2_authenticator.rb

@@ -34,13 +34,19 @@ class Net::IMAP::SASL::XOAuth2Authenticator
   # relying only the identity and scope authorized by the token.
   attr_reader :username
 
+  # Note that, unlike most other authenticators, #username is an alias for the
+  # authorization identity and not the authentication identity.  The
+  # authenticated identity is established for the client by the #oauth2_token.
+  alias authzid username
+
   # An OAuth2 access token which has been authorized with the appropriate OAuth2
   # scopes to use the service for #username.
   attr_reader :oauth2_token
 
   # :call-seq:
   #   new(username,  oauth2_token,  **) -> authenticator
   #   new(username:, oauth2_token:, **) -> authenticator
+  #   new(authzid:,  oauth2_token:, **) -> authenticator
   #
   # Creates an Authenticator for the "+XOAUTH2+" SASL mechanism, as specified by
   # Google[https://developers.google.com/gmail/imap/xoauth2-protocol],
@@ -50,13 +56,21 @@ class Net::IMAP::SASL::XOAuth2Authenticator
   # === Properties
   #
   # * #username --- the username for the account being accessed.
+  #
+  #   #authzid  --- an alias for #username.
+  #
+  #   Note that, unlike some other authenticators, +username+ sets the
+  #   _authorization_ identity and not the _authentication_ identity.  The
+  #   authenticated identity is established for the client with the OAuth token.
+  #
   # * #oauth2_token --- An OAuth2.0 access token which is authorized to access
   #   the service for #username.
   #
   # Any other keyword parameters are quietly ignored.
-  def initialize(user = nil, token = nil, username: nil, oauth2_token: nil, **)
-    @username = username || user or
-      raise ArgumentError, "missing username"
+  def initialize(user = nil, token = nil, username: nil, oauth2_token: nil,
+                 authzid: nil, **)
+    @username = authzid || username || user or
+      raise ArgumentError, "missing username (authzid)"
     @oauth2_token = oauth2_token || token or
       raise ArgumentError, "missing oauth2_token"
     [username, user].compact.count == 1 or

test/net/imap/test_imap_authenticators.rb

@@ -45,13 +45,34 @@ def test_plain_supports_initial_response
 
   def test_plain_response
     assert_equal("\0authc\0passwd", plain("authc", "passwd").process(nil))
+  end
+
+  def test_plain_authzid
     assert_equal("authz\0user\0pass",
                  plain("user", "pass", authzid: "authz").process(nil))
   end
 
+  def test_plain_kw_params
+    assert_equal(
+      "zid\0cid\0p",
+      plain(authcid: "cid", password: "p", authzid: "zid").process(nil)
+    )
+  end
+
+  def test_plain_username_kw_sets_both_authcid_and_authzid
+    assert_equal(
+      "\0uname\0passwd",
+      plain(username: "uname", password: "passwd").process(nil)
+    )
+  end
+
   def test_plain_no_null_chars
     assert_raise(ArgumentError) { plain("bad\0user", "pass") }
     assert_raise(ArgumentError) { plain("user", "bad\0pass") }
+    assert_raise(ArgumentError) { plain(authcid: "bad\0user", password: "p") }
+    assert_raise(ArgumentError) { plain(username: "bad\0user", password: "p") }
+    assert_raise(ArgumentError) { plain(username: "u", password: "bad\0pass") }
+    assert_raise(ArgumentError) { plain("u", "p", authzid: "bad\0authz") }
     assert_raise(ArgumentError) { plain("u", "p", authzid: "bad\0authz") }
   end
 
@@ -244,7 +265,11 @@ def test_external_matches_mechanism
 
   def test_external_response
     assert_equal("", external.process(nil))
+    assert_equal("", external.process(""))
     assert_equal("kwarg", external(authzid: "kwarg").process(nil))
+    assert_equal("username", external(username: "username").process(nil))
+    assert_equal("z", external("p", authzid: "z", username: "u").process(nil))
+    assert_equal("positional", external("positional").process(nil))
   end
 
   def test_external_utf8
@@ -256,7 +281,6 @@ def test_external_utf8
   def test_external_invalid
     assert_raise(ArgumentError) { external(authzid: "bad\0contains NULL") }
     assert_raise(ArgumentError) { external(authzid: "invalid utf8\x80") }
-    assert_raise(ArgumentError) { external("invalid positional argument") }
   end
 
   # ----------------------