I'd like to authenticate FTP clients either via username+password or a client certificate. Only FTPS is allowed.

User/password works, but while testing with curl (I don't have another option) and a client certificate, I need to pass a user. Isn't it technically possible to authenticate only by providing a certificate?

vsftpd.conf

passwd_chroot_enable=YES
chroot_local_user=YES
ssl_enable=YES
rsa_cert_file=usrlocal/ssl/certs/vsftpd.pem
force_local_data_ssl=YES
force_local_logins_ssl=YES

Tested with curl -v -k -E client-crt.pem --ftp-ssl-reqd ftp://server:21/testfile the output is:

* SSLv3, TLS handshake, Client hello (1):
* SSLv3, TLS handshake, Server hello (2):
* SSLv3, TLS handshake, CERT (11):
* SSLv3, TLS handshake, Request CERT (13):
* SSLv3, TLS handshake, Server finished (14):
* SSLv3, TLS handshake, CERT (11):
* SSLv3, TLS handshake, Client key exchange (16):
* SSLv3, TLS handshake, CERT verify (15):
* SSLv3, TLS change cipher, Client hello (1):
* SSLv3, TLS handshake, Finished (20):
* SSLv3, TLS change cipher, Client hello (1):
* SSLv3, TLS handshake, Finished (20):
* SSL connection using DES-CBC3-SHA
* Server certificate:
*        SSL certificate verify result: self signed certificate (18), continuing anyway.
> USER anonymous
< 530 Anonymous sessions may not use encryption.
* Access denied: 530
* Closing connection #0
* SSLv3, TLS alert, Client hello (1):
curl: (67) Access denied: 530

This is theoretically ok, as i forbid anonymous access. If I specify a user with -u username:pass it works, but it would without a certificate too.

The client certificate seems to be ok, it looks like this:

client-crt.pem

-----BEGIN RSA PRIVATE KEY-----
content
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
content
-----END CERTIFICATE-----

What am I missing? Thanks in advance. (The OS is Solaris 10 SPARC).