Safer handling of passwords on the command line (closes #408)

pom.xml

@@ -257,7 +257,7 @@
       <dependency>
         <groupId>info.picocli</groupId>
         <artifactId>picocli</artifactId>
-        <version>3.9.5</version>
+        <version>3.9.6</version>
       </dependency>
       <dependency>
         <groupId>org.apache.commons</groupId>

robozonky-app/src/main/java/com/github/robozonky/app/configuration/CommandLine.java

@@ -51,9 +51,9 @@ public class CommandLine implements Callable<Optional<InvestmentMode>> {
     private String notificationConfigLocation;
     @picocli.CommandLine.Option(names = {"-n", "--name"}, description = "Name of this RoboZonky session.")
     private String name = "Unnamed";
-    @picocli.CommandLine.Option(names = {"-p", "--password"}, required = true,
-            description = "Enter Zonky account password or secure storage password.")
-    private String password = null;
+    @picocli.CommandLine.Option(names = {"-p", "--password"}, required = true, interactive = true,
+            arity = "0..1", description = "Enter Zonky account password or secure storage password.")
+    private char[] password = null;
     @picocli.CommandLine.Option(names = {"-d", "--dry"},
             description = "RoboZonky will simulate investments, but never actually spend money.")
     private boolean dryRunEnabled = false;
@@ -119,7 +119,7 @@ Optional<URL> getNotificationConfigLocation() {
     }
 
     char[] getPassword() {
-        return password.toCharArray();
+        return password;
     }
 
     Optional<File> getKeystore() {

robozonky-app/src/main/java/com/github/robozonky/app/configuration/SecretProviderFactory.java

@@ -16,6 +16,7 @@
 
 package com.github.robozonky.app.configuration;
 
+import java.util.Arrays;
 import java.util.Optional;
 
 import com.github.robozonky.common.secrets.KeyStoreHandler;
@@ -37,14 +38,16 @@ private SecretProviderFactory() {
      * @return KeyStore-based secret provider or empty in case of a problem happened inside the keystore.
      */
     public static Optional<SecretProvider> getSecretProvider(final CommandLine cli) {
-        final char[] password = cli.getPassword();
         return cli.getKeystore().map(keystore -> {
+            final char[] password = cli.getPassword();
             try {
                 final KeyStoreHandler ksh = KeyStoreHandler.open(keystore, password);
                 return Optional.of(SecretProvider.keyStoreBased(ksh));
             } catch (final Exception ex) {
                 LOGGER.error("Failed opening guarded storage.", ex);
                 return Optional.<SecretProvider>empty();
+            } finally {
+                Arrays.fill(password, ' '); // clear the password from memory
             }
         }).orElseThrow(() -> new IllegalStateException("Could not find keystore."));
     }

robozonky-app/src/test/java/com/github/robozonky/app/configuration/SecretProviderFactoryTest.java

@@ -45,14 +45,16 @@ void nonexistentKeyStoreProvided() throws Exception {
     @Test
     void wrongFormatKeyStoreProvided() throws Exception {
         final File tmp = File.createTempFile("robozonky-", ".keystore"); // empty key store
-        final CommandLine cli = SecretProviderFactoryTest.mockCli(tmp, "password".toCharArray());
+        final char[] password = "pass".toCharArray();
+        final CommandLine cli = SecretProviderFactoryTest.mockCli(tmp, password);
         assertThat(SecretProviderFactory.getSecretProvider(cli)).isEmpty();
+        assertThat(password).isEqualTo("    ".toCharArray());
     }
 
     @Test
-    void noFallback() {
-        final String password = "pass";
-        final CommandLine cli = SecretProviderFactoryTest.mockCli(null, password.toCharArray());
+    void nullKeystoreProvided() {
+        final char[] password = "pass".toCharArray();
+        final CommandLine cli = SecretProviderFactoryTest.mockCli(null, password);
         assertThatThrownBy(() -> SecretProviderFactory.getSecretProvider(cli))
                 .isInstanceOf(IllegalStateException.class);
     }

robozonky-cli/src/main/java/com/github/robozonky/cli/KeyStoreLeveragingFeature.java

@@ -27,7 +27,7 @@ abstract class KeyStoreLeveragingFeature extends AbstractFeature {
             required = true)
     private File keystore = new File("robozonky.keystore");
     @CommandLine.Option(names = {"-s", "--secret"}, description = "Secret to use to access the keystore.",
-            required = true, interactive = true)
+            required = true, interactive = true, arity = "0..1")
     private char[] secret = null;
     private KeyStoreHandler storage;
 

robozonky-cli/src/main/java/com/github/robozonky/cli/MasterPasswordFeature.java

@@ -25,7 +25,8 @@ public final class MasterPasswordFeature extends KeyStoreLeveragingFeature {
 
     static final String DESCRIPTION = "Change password of the master keystore.";
     @CommandLine.Option(names = {"-n", "--new-secret"},
-            description = "Username to use to authenticate with Zonky servers.", required = true, interactive = true)
+            description = "Username to use to authenticate with Zonky servers.", required = true, interactive = true,
+            arity = "0..1")
     private char[] newSecret = null;
 
     public MasterPasswordFeature(final File keystore, final char[] keystoreSecret, final char... newSecret) {

robozonky-cli/src/main/java/com/github/robozonky/cli/ZonkoidPasswordFeature.java

@@ -31,7 +31,8 @@ public final class ZonkoidPasswordFeature extends KeyStoreLeveragingFeature {
     static final String ZONKOID_ID = "zonkoid";
     private final String id;
     @CommandLine.Option(names = {"-p", "--password"},
-            description = "Code generated in the Zonkoid mobile application.", required = true, interactive = true)
+            description = "Code generated in the Zonkoid mobile application.", required = true, interactive = true,
+            arity = "0..1")
     private char[] password = null;
 
     public ZonkoidPasswordFeature(final File keystore, final char[] keystoreSecret, final char... password) {

robozonky-cli/src/main/java/com/github/robozonky/cli/ZonkyPasswordFeature.java

@@ -33,7 +33,8 @@ public final class ZonkyPasswordFeature extends KeyStoreLeveragingFeature {
             description = "Username to use to authenticate with Zonky servers.", required = true)
     private String username = null;
     @CommandLine.Option(names = {"-p", "--password"},
-            description = "Password to use to authenticate with Zonky servers.", required = true, interactive = true)
+            description = "Password to use to authenticate with Zonky servers.", required = true, interactive = true,
+            arity = "0..1")
     private char[] password = null;
 
     public ZonkyPasswordFeature(final File keystore, final char[] keystoreSecret, final String username,