Credentials should be stored in EncryptedSharedPreferences

[ArnyminerZ]

Right now, credentials are being stored inside regular SharedPreferences in CalendarCredentials:

icsx5/app/src/main/java/at/bitfire/icsdroid/db/CalendarCredentials.kt

Lines 17 to 19 in 0b1443d

	private val credentialPrefs = context.getSharedPreferences(PREF_CREDENTIALS, 0)

EncryptedSharedPreferences shall be used.

The change is quite simple, they provide a good example:

MasterKey masterKey = new MasterKey.Builder(context)
     .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
     .build();

 SharedPreferences sharedPreferences = EncryptedSharedPreferences.create(
     context,
     "secret_shared_prefs",
     masterKey,
     EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
     EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
 );

 // use the shared preferences and editor as you normally would
 SharedPreferences.Editor editor = sharedPreferences.edit();

[ArnyminerZ]

Note the warning on the docs:

The preference file should not be backed up with Auto Backup. When restoring the file it is likely the key used to encrypt it will no longer be present. You should exclude all EncryptedSharedPreferences from backup using backup rules.

This means that we should provide an option to authorize back again after a device factory reset, or backup restore. Should be taken into account with #4.

Also security-crypto shall be added as dependency:

implementation "androidx.security:security-crypto:1.0.0"

[rfc2822]

When we have the database, I'd just store everything (including credentials) in the private DB. EncryptedSharedPreferences says that it doesn't work across system backup/restore on different devices, but this is a use case that is planned (#4).

Unfortunately we have to store the credentials in clear text for Basic authentication.

[ArnyminerZ]

Then we should store the accounts in Room instead of shared preferences for #76. This means creating a new table, and getting rid of CalendarCredentials.

[rfc2822]

Then we should store the accounts in Room instead of shared preferences for #76. This means creating a new table, and getting rid of CalendarCredentials.

Sounds reasonable :)

[ArnyminerZ]

The migration and tests for this have been added to #92 😄