docs: note CURLOPT_PINNEDPUBLICKEY has no effect on legacy LDAP backend

Closes #21682

diff --git a/docs/libcurl/opts/CURLOPT_PINNEDPUBLICKEY.md b/docs/libcurl/opts/CURLOPT_PINNEDPUBLICKEY.md
index 0590143c906bdb1394fd710755de5525449a03f6..82dd1626d140ee4c3c6a1a61a1b8eea3cab257d5 100644 (file)
--- a/docs/libcurl/opts/CURLOPT_PINNEDPUBLICKEY.md
+++ b/docs/libcurl/opts/CURLOPT_PINNEDPUBLICKEY.md
@@ -53,6 +53,11 @@ On mismatch, *CURLE_SSL_PINNEDPUBKEYNOTMATCH* is returned.
 The application does not have to keep the string around after setting this
 option.
 
+This option has no effect on LDAP connections when libcurl uses the legacy LDAP
+backend. That backend manages TLS independently of curl's TLS layer. When
+libcurl is built with USE_OPENLDAP, the OpenLDAP backend routes TLS through
+curl's layer and this option is honored.
+
 # DEFAULT
 
 NULL