here is how to set a read-only for some groups
and read-write for another group.

the obvious

<Location /dav/>
    <LimitExcept GET POST OPTIONS PROPFIND>
    Require group internal
    </LimitExcept>

require group internal client1
</Location>

does not work



<Location /dav/>
    Dav on      
    <LimitExcept GET POST OPTIONS PROPFIND>
    Require group internal
    </LimitExcept>

   <Limit GET POST OPTIONS PROPFIND>
    Require group internal client1
    </Limit>

    AuthType Basic
    AuthName "dav here"
    AuthUserFile htpasswd
    AuthGroupFile htgroup
</Location>