In ProFTPd, how to set different permissions for different virtual users?

Question

How do I set different permissions to different virtual users in ProFTPd?

I created several users with the ftpasswd command, but for now they all have permissions to both read and write to their respective folders. I want to keep those full permissions for some users, but restrict some other users to read-only. Tried googling and reading official documentation, but I can't find any relevant info.

Here's my proftpd.conf, if that helps:

DefaultRoot                     ~
ServerIdent                     on "FTP Server ready."
RootLogin                       off
AllowOverwrite                  on
RequireValidShell               off
AuthUserFile                    /etc/proftpd/ftpd.passwd
LogFormat                       default «%h %l %u %t «%r» %s %b»
LogFormat                       auth    «%v [%P] %h %t «%r» %s»
LogFormat                       write   «%h %l %u %t «%r» %s %b»

SystemLog                       /var/log/proftpd/proftpd.log
TransferLog                     /var/log/proftpd/xfer.log
ExtendedLog                     /var/log/proftpd/access.log WRITE,READ write
ExtendedLog                     /var/log/proftpd/auth.log AUTH auth

ServerName                      "ProFTPD Default Installation"
ServerType                      standalone
DefaultServer                   on

Port                            21
UseIPv6                         off
Umask                           022
MaxInstances                    30

# Set the user and group under which the server will run.
User                            nobody
Group                           nobody

# Normally, we want files to be overwriteable.
AllowOverwrite          on

# Bar use of SITE CHMOD by default
<Limit SITE_CHMOD>
  DenyAll
</Limit>

#############
# SFTP ZONE #
#############

<VirtualHost 0.0.0.0>
  <IfModule mod_sftp.c>
    DefaultRoot ~
    RootLogin off
    AllowOverwrite on
    AuthUserFile /etc/proftpd/ftpd.passwd
    RequireValidShell off

    SFTPEngine on
    Port 2122
    SFTPLog /var/log/proftpd/sftp.log
    SFTPHostKey /etc/ssh/ssh_host_rsa_nopass
    SFTPAuthMethods password
    SFTPOptions AllowInsecureLogin

    ServerIdent on "FTP Server ready."
    TransferLog /var/log/proftpd/xfer.log
    ExtendedLog /var/log/proftpd/access.log WRITE,READ write
    ExtendedLog /var/log/proftpd/auth.log AUTH auth
  </IfModule>
</VirtualHost>

So, how do I allow writing to their directories for some users, but forbid it to others? Just in case, I don't want to allow anonymous users, so I'm looking for a solution that doesn't include allowing anonymous login