Something

<VirtualHost *:80>
    ServerName svn.foo.com
    Alias /trac/ /usr/local/share/trac/htdocs/
    DocumentRoot "/usr/local/trac/"

    RewriteEngine on
    RewriteRule ^/projects/+$                       /projects/index.html [L]
    RewriteCond /usr/local/trac/env/$1              -d
    RewriteRule ^/projects/([[:alnum:]]+)(/?.*)     /projects/trac.cgi$2 [S=1,E=TRAC_ENV:/usr/local/trac/env/$1]
    RewriteRule ^/projects/(.*)                     /projects/index.html

    <Location "/cgi-bin/trac.cgi">
        SetEnv TRAC_ENV "/usr/local/trac/env"
    </Location>

    <Location /repos>
        DAV svn
        SVNPath /usr/local/svnroot
    </Location>

    #You have to allow people to read the files in htdocs
    <Directory "/usr/local/share/trac/htdocs">
        Options Indexes MultiViews
        AllowOverride None
        Order allow,deny
        Allow from all
    </Directory>
    <Directory "/usr/local/trac/projects">
        AllowOverride None
        Options ExecCGI -MultiViews +SymLinksIfOwnerMatch
        AddHandler cgi-script .cgi
        Order allow,deny
        Allow from all
    </Directory>

#    <LocationMatch "/projects/[[:alnum:]]+/login">
#           AuthType Basic
#           AuthName "trac"
#           AuthUserFile /usr/local/apache2/passwords
#           Require valid-user
#    </LocationMatch>
#
 </VirtualHost>