Unable to read the CA certificate set by LDAPTrustedGlobalCert

Issue

To connect to the LDAP server using ldaps, I have set LDAPTrustedGlobalCert to /path/to/certs/cacert.pem, but no success.
When setting LDAPLibraryDebug to 7, the following log message appears in the error_log:

TLS: could not load verify locations (file:`/path/to/certs/cacert.pem',dir:`').
TLS: error:8000000D:system library::Permission denied crypto/bio/bss_file.c:67
TLS: error:10080002:BIO routines::system lib crypto/bio/bss_file.c:77
TLS: error:05880002:x509 certificate routines::system lib crypto/x509/by_file.c:228
TLS: init_def_ctx: error:8000000D:system library::Permission denied.