Prompt you to enter the keystore password if you forget before starting a new Android build in Unity.

AutoPasswordPrompt.cs

using UnityEngine;
using UnityEditor;
using UnityEditor.Build;

public class AutoPasswordPrompt : EditorWindow {

    [InitializeOnLoadMethod]
    static void Register() => BuildPlayerWindow.RegisterBuildPlayerHandler(BuildHandler);

    static bool IsUnfilled() =>
        string.IsNullOrEmpty(PlayerSettings.Android.keystorePass) ||
        string.IsNullOrEmpty(PlayerSettings.Android.keyaliasPass);

    static void BuildHandler(BuildPlayerOptions options) {
        if (options.target == BuildTarget.Android &&
            PlayerSettings.Android.useCustomKeystore &&
            IsUnfilled() &&
            EditorUtility.DisplayDialog(
                "Password Prompt",
                "You have not set the keystore password or the key alias password. Do you want to set it now?",
                "Yes", "No"
            )
        ) {
            GetWindow<AutoPasswordPrompt>("Keystore Password").ShowModalUtility();
            if (IsUnfilled()) throw new BuildFailedException("Keystore password and key alias password not set.");
        }
        BuildPlayerWindow.DefaultBuildMethods.BuildPlayer(options);
    }

    void OnGUI() {
        GUILayout.Label("Please enter the keystore password and the key alias password.");
        var keystorePass = PlayerSettings.Android.keystorePass;
        using (var changed = new EditorGUI.ChangeCheckScope()) {
            keystorePass = EditorGUILayout.PasswordField(PlayerSettings.Android.keystoreName, keystorePass);
            if (changed.changed) PlayerSettings.Android.keystorePass = keystorePass;
        }
        var keyaliasPass = PlayerSettings.Android.keyaliasPass;
        using (var changed = new EditorGUI.ChangeCheckScope()) {
            keyaliasPass = EditorGUILayout.PasswordField(PlayerSettings.Android.keyaliasName, keyaliasPass);
            if (changed.changed) PlayerSettings.Android.keyaliasPass = keyaliasPass;
        }
        if (GUILayout.Button("Done")) Close();
    }
}