The userAttr needs to be the full DN, otherwise the search does not work:
```
❯ ldapsearch -x -H ldap://localhost:3890 -D "cn=admin,ou=people,dc=example,dc=com" -b "ou=groups,dc=example,dc=com" -W "member=bob"
Enter LDAP Password:
# extended LDIF
#
# LDAPv3
# base <ou=groups,dc=example,dc=com> with scope subtree
# filter: member=bob
# requesting: ALL
#
# search result
search: 2
result: 53 Server is unwilling to perform
text: Unsupported group filter: while parsing a user ID: Missing DN value
# numResponses: 1
```
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