audrey/src/ui/setup.vala

static void salt_password (string password, out string token, out string salt) {
    const int SALT_BYTES = 8;
    uchar salt_bytes[SALT_BYTES];
    GCrypt.Random.randomize (salt_bytes, GCrypt.Random.Level.STRONG);
    uchar salt_chars[2*SALT_BYTES+1];
    for (int i = 0; i < SALT_BYTES; i += 1) {
        salt_chars[2*i+0] = "0123456789abcdef"[(salt_bytes[i]>>4)&0xf];
        salt_chars[2*i+1] = "0123456789abcdef"[(salt_bytes[i]>>0)&0xf];
    }
    salt_chars[2*SALT_BYTES] = 0;
    var checksum = new GLib.Checksum (ChecksumType.MD5);
    checksum.update ((uchar[]) password, -1);
    checksum.update (salt_chars, -1);

    token = checksum.get_string ();
    salt = (string) salt_chars;
}

[GtkTemplate (ui = "/eu/callcc/audrey/ui/setup.ui")]
public class Ui.Setup : Adw.PreferencesDialog {
    public string status { get; private set; default = _("Not connected"); }

    public bool authn_can_edit { get; private set; default = true; }
    public bool authn_can_validate { get; private set; default = false; }

    public string server_url { get; set; default = ""; }
    public string username { get; set; default = ""; }
    public string password { get; set; default = ""; }
    public string token;
    public string salt;

    public signal void connected (Subsonic api);

    private static Secret.Schema secret_schema = new Secret.Schema (
        "eu.callcc.audrey",
        Secret.SchemaFlags.NONE,
        "server-url", Secret.SchemaAttributeType.STRING,
        "username", Secret.SchemaAttributeType.STRING
    );

    [GtkCallback] private void on_authn_changed () {
        this.authn_can_validate = true;
    }

    [GtkCallback] private void on_authn_validate_activated () {
        this.authn_can_validate = false;
        this.authn_can_edit = false;
        this.status = _("Connecting...");

        string new_token, new_salt;
        salt_password (this.password, out new_token, out new_salt);
        var api = new Subsonic.with_token (
            this.server_url,
            this.username,
            new_token,
            new_salt);

        api.ping.begin ((obj, res) => {
            try {
                api.ping.end (res);
                this.status = _("Connected");
                this.token = new_token;
                this.salt = new_salt;
                this.save ();

                this.connected (api);
            } catch (Error e) {
                this.status = @"$(_("Ping failed")): $(e.message)";
                this.authn_can_validate = true;
            }

            this.authn_can_edit = true;
        });
    }

    public void load () {
        this.authn_can_edit = false;
        Secret.password_searchv.begin (
            secret_schema,
            new HashTable<string, string> (null, null),
            Secret.SearchFlags.NONE,
            null,
            (obj, res) => {
                try {
                    var list = Secret.password_searchv.end (res);
                    if (list == null) {
                        // didn't find shit, leave all empty
                        this.server_url = "";
                        this.username = "";
                        this.password = "";
                        // TODO: onboarding
                        this.authn_can_edit = true;
                        this.authn_can_validate = true;
                    } else {
                        var first = list.data;
                        assert (first != null);

                        this.server_url = first.attributes["server-url"];
                        this.username = first.attributes["username"];

                        first.retrieve_secret.begin (null, (obj, res) => {
                            try {
                                var value = first.retrieve_secret.end (res);
                                this.password = value.get_text () ?? "";
                            } catch (Error e) {
                                error ("could not retrieve password from credentials: %s", e.message);
                            }

                            // first connection
                            this.authn_can_validate = true;
                            this.on_authn_validate_activated ();
                        });
                    }
                } catch (Error e) {
                    error ("could not search for password in keyring: %s", e.message);
                }
            });
    }

    public void save () {
        this.authn_can_edit = false;
        Secret.password_store.begin (secret_schema, null, "Audrey Subsonic password", this.password, null, (obj, res) => {
            try {
                Secret.password_store.end (res);
            } catch (Error e) {
                error ("could not store password in keyring: %s", e.message);
            }
            this.authn_can_edit = true;
        }, "server-url", this.server_url, "username", this.username);
    }
}