Add user tag prefix to in_forward plugin

[nanorobocop]

Is your feature request related to a problem? Please describe.

Hello,

We're trying to use forward plugin for multi-tenant configuration. So each tenant would have it's own username and password. It is basically described in in_forward_users.conf and out_forward_users.conf config examples. What we also want - is to ensure that tenant1 won't send (audit) logs on behalf tenant2. So, want to add user_tag_prefix to security section on server side (in_forward).

Describe the solution you'd like

Current configuration (in_forward_users.conf):

<source>
  @type forward
  <security>
    self_hostname input.testing.local
    shared_key    secure_communication_is_awesome
    user_auth     yes
    <user>
      username user1
      password yes_this_is_user1
    </user>
    <user>
      username user2
      password yes_this_is_really_user2
    </user>
  </security>
</source>

Desired configuration:

<source>
  @type forward
  <security>
    self_hostname input.testing.local
    shared_key    secure_communication_is_awesome
    user_auth     yes
    user_tag_prefix     yes                   #### NEW
    <user>
      username user1
      password yes_this_is_user1
    </user>
    <user>
      username user2
      password yes_this_is_really_user2
    </user>
  </security>
</source>

As a result, tag would have prefix with username:

Original tag coming from user1: auditlog Desired tag after user_tag_prefix: user1.auditlog

Describe alternatives you've considered

Nothing

Additional context

No response

[nanorobocop]

There's actually also add_tag_prefix, but not in <security> section. Wondering, if need to combine it with user_tag_prefix. For example, using $username value. There probably should be logic for cases:

• If user_auth enabled
• If allow_anonymous_source enabled