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Can't contact LDAP server with Google WorkspaceLDAP

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yetty

I try to test the connection to the Google Workspace LDAP server. I follow this help page: https://support.google.com/a/answer/9190869?hl=en#ldap-query&zippy=%2Cldapsearch

But when I run the suggested commands, I get this error:

root@debian:/etc/freeradius/3.0# LDAPTLS_CERT=/etc/freeradius/3.0/certs/ldap-client.crt LDAPTLS_KEY=/etc/freeradius/3.0/certs/ldap-client.key ldapsearch -v -H ldaps://ldap.google.com:636 -b dc=MYDOMAIN,dc=cz '([email protected])'
ldap_initialize( ldaps://ldap.google.com:636/??base )
ldap_sasl_interactive_bind_s: Can't contact LDAP server (-1)
    additional info: (unknown error code)

Any idea what's wrong?

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Andrew Grasso avatar Server
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Andrew Grasso

On Ubuntu 20.04 I found that I had to disable TLS1.3 by setting LDAPTLS_CIPHER_SUITE='NORMAL:!VERS-TLS1.3' to get ldapsearch working against Google LDAP.

How I got here:

The ldapsearch command supports printing increased debug to the console by using the -d debuglevel flag. Debug level 1 (-d1) was enough for me, higher debug levels get very verbose and hard to read.

A simple debug command might look like this:

vagrant@focal:~$ ldapsearch -H ldaps://ldap.google.com:636 -d1

From here I could see that the certificate was untrusted:

...
attempting to connect:
connect success
TLS: peer cert untrusted or revoked (0x42)
TLS: can't connect: (unknown error code).
...

This didn't make any sense. The certificate being returned by ldap.google.com was valid and could be verified against my /etc/ssl/certs/ca-certificates.crt using openssl s_client -connect ldap.google.com:636 -CAfile /etc/ssl/certs/ca-certificates.crt but ldapsearch didn't trust it.

I finally came across this post on the OpenLDAP mailing list which explained the problem was with SNI not being supported which would cause Google to return an invalid self-signed cert. I wasn't able to find a proper fix, but the workaround at the bottom to disable TLS1.3 by setting the LDAPTLS_CIPHER_SUITE environment variable worked for me because my OpenLDAP was using GnuTLS. If you're using OpenSSL you'll likely need to find a different workaround, but the root cause is probably still the same.

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