M_INVALID_USERNAME when setting a profile from IRC to Matrix

Describe the bug

I am getting M_INVALID_USERNAME errors when joining a bridging a IRC room with membershipLists synced

Jul 25 10:27:11 neocarie node[56160]: 2021-07-25 10:27:11 INFO:req [5gu6dhb121400] [[I->M]] onJoin(names) toto[z] to #general
Jul 25 10:27:11 neocarie node[56160]: 2021-07-25 10:27:11 INFO:IrcBridge irc_toto[z] does not exist in the store yet, setting a profile
Jul 25 10:27:11 neocarie node[56160]: 2021-07-25 10:27:11 INFO:IrcBridge [-] POST https://matrix.[DOMAIN]:8448/_matrix/client/r0/register (AS) Body: "{\"type\":\"m.login.application_service\",\"username\":\"irc_toto[z]\"}"
Jul 25 10:27:11 neocarie node[56160]: 2021-07-25 10:27:11 ERROR:IrcBridge [-] POST https://matrix.[DOMAIN]:8448/_matrix/client/r0/register (AS) HTTP 400 Error: "{\"errcode\":\"M_INVALID_USERNAME\",\"error\":\"Username can only contain characters a-z, 0-9, or '_-./='\"}"

([DOMAIN] is my domain name that I removed from the logs)

Configuration

# Configuration specific to AS registration. Unless other marked, all fields
# are *REQUIRED*.
# Unless otherwise specified, these keys CANNOT be hot-reloaded.
homeserver:
  # The URL to the home server for client-server API calls, also used to form the
  # media URLs as displayed in bridged IRC channels:
  url: "https://matrix.[DOMAIN]:8448"

  # The 'domain' part for user IDs on this home server. Usually (but not always)
  # is the "domain name" part of the HS URL.
  domain: "[DOMAIN]"

  # Should presence be enabled for matrix clients on this bridge. If disabled on the
  # homeserver then it should also be disabled here to avoid excess traffic.
  # Default: true
  enablePresence: false

  # Which port should the appservice bind to. Can be overriden by the one provided in the
  # command line! Optional.
  bindPort: 8009

  # Use this option to force the appservice to listen on another hostname for transactions.
  # This is NOT your synapse hostname. E.g. use 127.0.0.1 to only listen locally. Optional.
  bindHostname: 127.0.0.1

# Configuration specific to the IRC service
ircService:
  # All server keys can be hot-reloaded, however existing IRC connections
  # will not have changes applied to them.
  servers:
    # The address of the server to connect to.
    irc.[DOMAIN]:
      # A human-readable short name. This is used to label IRC status rooms
      # where matrix users control their connections.
      # E.g. 'ExampleNet IRC Bridge status'.
      # It is also used in the Third Party Lookup API as the instance `desc`
      # property, where each server is an instance.
      name: "[DOMAIN]"
      # Additional addresses to connect to, used for load balancing between IRCDs.
      additionalAddresses: []
      # Typically additionalAddresses would be in addition to the address key given above,
      # but some configurations wish to exclusively use additional addresses while reserving
      # the top key for identification purposes. Set this to true to exclusively use the
      # additionalAddresses array when connecting to servers.
      onlyAdditionalAddresses: false

      # The port to connect to. Optional.
      port: 6697
      # Whether to use SSL or not. Default: false.
      ssl: true
      # Whether or not IRC server is using a self-signed cert or not providing CA Chain
      sslselfsign: true

      # A map for conversion of IRC user modes to Matrix power levels. This enables bridging
      # of IRC ops to Matrix power levels only, it does not enable the reverse. If a user has
      # been given multiple modes, the one that maps to the highest power level will be used.
      modePowerMap:
        o: 50
        v: 1

      botConfig:
        # Enable the presence of the bot in IRC channels. The bot serves as the entity
        # which maps from IRC -> Matrix. You can disable the bot entirely which
        # means IRC -> Matrix chat will be shared by active "M-Nick" connections
        # in the room. If there are no users in the room (or if there are users
        # but their connections are not on IRC) then nothing will be bridged to
        # Matrix. If you're concerned about the bot being treated as a "logger"
        # entity, then you may want to disable the bot. If you want IRC->Matrix
        # but don't want to have TCP connections to IRC unless a Matrix user speaks
        # (because your client connection limit is low), then you may want to keep
        # the bot enabled. Default: true.
        # NB: If the bot is disabled, you SHOULD have matrix-to-IRC syncing turned
        #     on, else there will be no users and no bot in a channel (meaning no
        #     messages to Matrix!) until a Matrix user speaks which makes a client
        #     join the target IRC channel.
        # NBB: The bridge bot IRC client will still join the target IRC network so
        #      it can service bridge-specific queries from the IRC-side e.g. so
        #      real IRC clients have a way to change their Matrix display name.
        #      See https://github.com/matrix-org/matrix-appservice-irc/issues/55
        enabled: false

      # Configuration for PMs / private 1:1 communications between users.
      privateMessages:
        # Enable the ability for PMs to be sent to/from IRC/Matrix.
        # Default: true.
        enabled: true

      # Configuration for mappings not explicitly listed in the 'mappings'
      # section.
      dynamicChannels:
        # Enable the ability for Matrix users to join *any* channel on this IRC
        # network.
        # Default: false.
        enabled: true
        # The room alias template to apply when creating new aliases. This only
        # applies if createAlias is 'true'. The following variables are exposed:
        # $SERVER => The IRC server address (e.g. "irc.example.com")
        # $CHANNEL => The IRC channel (e.g. "#python")
        # This MUST have $CHANNEL somewhere in it.
        #
        # In certain circumstances you might want to bridge your whole IRC network as a
        # homeserver (e.g. #matrix:libera.chat). For these use cases, you can set the
        # template to just be $CHANNEL. Doing so will preclude you from supporting
        # other prefix characters though.
        #
        # Default: '#irc_$SERVER_$CHANNEL'
        aliasTemplate: "$CHANNEL"

      # Configuration for controlling how Matrix and IRC membership lists are
      # synced.
      membershipLists:
        # Enable the syncing of membership lists between IRC and Matrix. This
        # can have a significant effect on performance on startup as the lists are
        # synced. This must be enabled for anything else in this section to take
        # effect. Default: false.
        enabled: true

        global:
          ircToMatrix:
            # Get a snapshot of all real IRC users on a channel (via NAMES) and
            # join their virtual matrix clients to the room.
            initial: true
            # Make virtual matrix clients join and leave rooms as their real IRC
            # counterparts join/part channels. Default: false.
            incremental: true
            # Should the bridge check if all Matrix users are connected to IRC and
            # joined to the channel before relaying messages into the room.
            #
            # This is considered a safety net to avoid any leakages by the bridge to
            # unconnected users, but given it ignores all IRC messages while users
            # are still connecting it may be overkill.
            requireMatrixJoined: true

          matrixToIrc:
            # Get a snapshot of all real Matrix users in the room and join all of
            # them to the mapped IRC channel on startup. Default: false.
            initial: true
            # Make virtual IRC clients join and leave channels as their real Matrix
            # counterparts join/leave rooms. Make sure your 'maxClients' value is
            # high enough! Default: false.
            incremental: true

      # Configuration for virtual matrix users. The following variables are
      # exposed:
      # $NICK => The IRC nick
      # $SERVER => The IRC server address (e.g. "irc.example.com")
      matrixClients:
        # The user ID template to use when creating virtual matrix users. This
        # MUST have $NICK somewhere in it.
        # Optional. Default: "@$SERVER_$NICK".
        # Example: "@irc.example.com_Alice:example.com"
        userTemplate: "@irc_$NICK"
        # The display name to use for created matrix clients. This should have
        # $NICK somewhere in it if it is specified. Can also use $SERVER to
        # insert the IRC domain.
        # Optional. Default: "$NICK (IRC)". Example: "Alice (IRC)"
        displayName: "$NICK"

      # Configuration for virtual IRC users. The following variables are exposed:
      # $LOCALPART => The user ID localpart ("alice" in @alice:localhost)
      # $USERID => The user ID
      # $DISPLAY => The display name of this user, with excluded characters
      #             (e.g. space) removed. If the user has no display name, this
      #             falls back to $LOCALPART.
      ircClients:
        # The template to apply to every IRC client nick. This MUST have either
        # $DISPLAY or $USERID or $LOCALPART somewhere in it.
        # Optional. Default: "M-$DISPLAY". Example: "M-Alice".
        nickTemplate: "$DISPLAY"
        # True to allow virtual IRC clients to change their nick on this server
        # by issuing !nick <server> <nick> commands to the IRC AS bot.
        # This is completely freeform: it will NOT follow the nickTemplate.
        allowNickChanges: true
        # The max number of IRC clients that will connect. If the limit is
        # reached, the client that spoke the longest time ago will be
        # disconnected and replaced.
        # Optional. Default: 30.
        maxClients: 500
        # The number of lines to allow being sent by the IRC client that has received
        # a large block of text to send from matrix. If the number of lines that would
        # be sent is > lineLimit, the text will instead be uploaded to matrix and the
        # resulting URI is treated as a file. As such, a link will be sent to the IRC
        # side instead of potentially spamming IRC and getting the IRC client kicked.
        # Default: 3.
        lineLimit: 10
        # Choose which conditions the IRC bridge should kick Matrix users for. Decisions to this from
        # defaults should be taken with care as it may dishonestly repesent Matrix users on the IRC
        # network, and cause your bridge to be banned.
        kickOn:
          # Kick a Matrix user from a bridged room if they fail to join the IRC channel.
          channelJoinFailure: true
          # Kick a Matrix user from ALL rooms if they are unable to get connected to IRC.
          ircConnectionFailure: true
          # Kick a Matrix user from ALL rooms if they choose to QUIT the IRC network.
          userQuit: true

  # Configuration for logging. Optional. Default: console debug level logging
  # only.
  # This key CANNOT be hot-reloaded
  logging:
    # Level to log on console/logfile. One of error|warn|info|debug
    level: "info"

# Use an external database to store bridge state.
# This key CANNOT be hot-reloaded.
database:
  # database engine (must be 'postgres' or 'nedb'). Default: nedb
  engine: "postgres"
   # Either a PostgreSQL connection string, or a path to the NeDB storage directory.
   # For postgres, it must start with postgres://
   # For NeDB, it must start with nedb://. The path is relative to the project directory.
  connectionString: "postgres://matrix-appservice-irc:CHANGE_ME@localhost:5432/matrix-appservice-irc"

The appservice works and I am able to send and receive messages from both ends. The appservice bot user is buggy (can not invite and does not respond to !help), but I believe that's a separate issue.

Expected behavior I would expect the appservice to normalize IRC usernames to make them fit the Matrix constraints.

Server:

OS: Debian Bullseye with NodeJS 14 from experimental
Homeserver: Dendrite 0.4.0

matrix-org / matrix-appservice-irc

M_INVALID_USERNAME when setting a profile from IRC to Matrix #1432