Add UI option to choose between the different backends to save passwords on Linux

[purejava]

Cryptomator has the ability to save passwords in system keychains.
On Linux, this does work for the GNOME desktop environment and KDE.
To be precise: either gnome-keyring or kwalletd needs to be installed and configured, as they function as the backends to store passwords.

Right now, Cryptomator tests on start-up, if either one of the two is available and uses this backend from then on.

cryptomator/main/keychain/src/main/java/org/cryptomator/keychain/LinuxSystemKeychainAccess.java

Lines 25 to 36 in 817907c

	private static Optional<KeychainAccessStrategy> constructKeychainAccess() {
	try { // is kwallet or gnome-keyring installed?
	Class<?> clazz = Class.forName("org.cryptomator.keychain.LinuxKDEWalletKeychainAccessImpl");
	KeychainAccessStrategy instance = (KeychainAccessStrategy) clazz.getDeclaredConstructor().newInstance();
	if (instance.isSupported()) return Optional.of(instance);
	clazz = Class.forName("org.cryptomator.keychain.LinuxSecretServiceKeychainAccessImpl");
	instance = (KeychainAccessStrategy) clazz.getDeclaredConstructor().newInstance();
	return Optional.of(instance);
	} catch (Exception e) {
	return Optional.empty();
	}
	}

It would be nice, if there was an UI option to choose and change on the fly, which backend should be used.

This idea occurred here.

[purejava]

We need the changes for secret-service described here being released, before we can implement this new feature.

[purejava]

Design decision

Would you prefer an application wide setting or per vault, to change between the different backends while on Linux?

[tobihagemann]

Not an easy decision at all. I would've thought that an application-wide setting would be the least confusing because you usually won't use multiple keychains for the same application. However, we don't have anything password/keychain-related in "Preferences" yet. But we do have a password section in "Vault Options". Hm... @overheadhunter, what do you think?

[overheadhunter]

Should be application-wide. The only reason I can think of, why one should use different keychains for different vaults is due to legacy keychain entries from before kwallet support was added. Affected users can then still migrate this manually. Normally there should be only one keychain in use.

[BeyerMart]

Yes, I agree with this perspective.
I think one would like to use a keychain for all the same vaults.

[tobihagemann]

All right, I guess it's a "General" dropdown setting in the application-wide "Preferences" then. 😄

[purejava]

Thanks for the directions. 😃👏🏻

[BeyerMart]

Wow @purejava your solution looks great. Thank you for your contribution.
I tried to store a List of Optional as "delegate", but that would mean refactoring every method of LinuxSystemKeychainAccess.

[purejava]

Thanks for the flowers @BeyerMart! 😃
The change is still under development and I'll explain the design desicions in the upcoming PR and let you comment on the change.

[overheadhunter]

Fixed in #1375 (Linux) and refined in #1393 (for macOS, Windows)