Depois de muitas tentativas, encontrei a solução. O problema estava na configuração incorreta do VirtualHost para git-http-backend.
Aqui está minha configuração de trabalho:
<IfModule mod_ssl.c>
<VirtualHost _default_:443>
DocumentRoot /git/myrepos
SetEnv GIT_PROJECT_ROOT /git/myrepos
SetEnv GIT_HTTP_EXPORT_ALL
ScriptAlias /myrepos/ /usr/lib/git-core/git-http-backend
AliasMatch ^/myrepos/(.*/objects/[0-9a-f]{2}/[0-9a-f]{38})$ /git/myrepos/$1
AliasMatch ^/repos/(.*/objects/pack/pack-[0-9a-f]{40}.(pack|idx))$ /git/myrepos/$1
ScriptAliasMatch "(?x)^/(.*/(HEAD | info/refs | objects/(info/[^/]+ | [0-9a-f]{2}/[0-9a-f]{38} | pack/pack-[0-9a-f]{40}\.(pack|idx)) | git-(upload|receive)-pack))$" /usr/lib/git-core/git-http-backend/$1
<Directory "/usr/lib/git-core/">
Options +ExecCGI
Allow From All
</Directory>
ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
<Directory "/usr/lib/cgi-bin">
AllowOverride None
Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
Order allow,deny
Allow from all
</Directory>
ErrorLog ${APACHE_LOG_DIR}/error.log
LogLevel warn
CustomLog ${APACHE_LOG_DIR}/ssl_access.log combined
SSLEngine on
SSLCertificateFile /etc/ssl/git.crt
SSLCertificateKeyFile /etc/ssl/git.key
<FilesMatch "\.(cgi|shtml|phtml|php)$">
SSLOptions +StdEnvVars
</FilesMatch>
<Directory /usr/lib/cgi-bin>
SSLOptions +StdEnvVars
</Directory>
BrowserMatch "MSIE [2-6]" \
nokeepalive ssl-unclean-shutdown \
downgrade-1.0 force-response-1.0
BrowserMatch "MSIE [17-9]" ssl-unclean-shutdown
<Location /repo1.git>
Order deny,allow
Deny from all
Allow from all
AuthName "GIT Authentication"
AuthType Basic
AuthBasicProvider ldap
AuthzLDAPAuthoritative off
AuthLDAPBindDN domain\user
AuthLDAPBindPassword passwd
AuthLDAPURL ldap://ldap.server:389/ou=git,DC=domain?sAMAccountName
Require ldap-group cn=git_repo1,ou=git,dc=domain
</Location>
</VirtualHost>
</IfModule>
Agora todas as operações do git funcionam corretamente com o git-http-backend via https com a autorização do ldap:)
Talvez isso seja útil para alguém.