# SSL and certificate validation

All SSL configuration is done per-storage.

## Pinning by fingerprint

To pin the certificate by fingerprint:

    [storage foo]
    type = "caldav"
    ...
    verify_fingerprint = "94:FD:7A:CB:50:75:A4:69:82:0A:F8:23:DF:07:FC:69:3E:CD:90:CA"
    #verify = false  # Optional: Disable CA validation, useful for self-signed certs

SHA1-, SHA256- or MD5-Fingerprints can be used. They’re detected by their length.

You can use the following command for obtaining a SHA-1 fingerprint:

    echo -n | openssl s_client -connect unterwaditzer.net:443 | openssl x509 -noout -fingerprint

Note that `verify_fingerprint` doesn’t suffice for vdirsyncer to work with self-signed certificates (or certificates that are not in your trust store). You most likely need to set `verify = false` as well. This disables verification of the SSL certificate’s expiration time and the existence of it in your trust store, all that’s verified now is the fingerprint.

However, please consider using Let’s Encrypt such that you can forget about all of that. It is easier to deploy a free certificate from them than configuring all of your clients to accept the self-signed certificate.

## Custom root CAs

To point vdirsyncer to a custom set of root CAs:

    [storage foo]
    type = "caldav"
    ...
    verify = "/path/to/cert.pem"

Vdirsyncer uses the requests library, which, by default, uses its own set of trusted CAs.

However, the actual behavior depends on how you have installed it. Many Linux distributions patch their `python-requests` package to use the system certificate CAs. Normally these two stores are similar enough for you to not care.

But there are cases where certificate validation fails even though you can access the server fine through e.g. your browser. This usually indicates that your installation of the `requests` library is somehow broken. In such cases, it makes sense to explicitly set `verify` or `verify_fingerprint` as shown above.

## Client Certificates

Client certificates may be specified with the `auth_cert` parameter. If the key and certificate are stored in the same file, it may be a string:

    [storage foo]
    type = "caldav"
    ...
    auth_cert = "/path/to/certificate.pem"

If the key and certificate are separate, a list may be used:

    [storage foo]
    type = "caldav"
    ...
    auth_cert = ["/path/to/certificate.crt", "/path/to/key.key"]