Best practice for securing web API endpoint

Say, I am working for a bank that lets users use a mobile app. I am a developer working on the mobile app for that bank. The app gets OAuth access token and access a web API hosted by the bank. The app has been released.

A regular user who has a valid account in the bank installs the mobile app. Through the mobile app, the user can view the balance, transfer money, etc.

This user has a dev skill and noticed that he can get the access token after he signs in to the bank with his user name and password.

Because this user has a valid account for the bank, the access token is valid to call the API endpoints. The user does trial and error in his Visual Studio to figure out what requests need to be sent to get a valid response from the API. He can refresh access token as many times as needed with the official mobile app manually and eventually finds a way to make valid calls against the API from his dev tool.

Question is, are there any mechanisms that can be utilized to prevent the user from calling the endpoint without going through the official mobile app? The web API can be marked with [RequiredScope] attribute, for example, but if he was able to sign in, should he have all the permissions to do what the normal users are allowed to do, such as transferring money?

I have done searches on this topic on the web as it seems to be a common topic, but have not found references yet.

Read answers here.

Resources

https://learn.microsoft.com/en-us/aspnet/core/security/authorization/secure-data?view=aspnetcore-6.0

FIDO2 and WebAuthn

Authentication has been an essential part of applications for some time now because applications need to know some information about the user who’s using the application. For the longest time, the solution to this has been username and passwords. Username passwords are popular because they’re convenient to implement. But they aren’t secure. There are many issues with passwords.

First, there’s the problem of transmitting this password securely. If you send the password over the wire, a man-in-the-middle could sniff it. That pretty much necessitated SSL over such communication or the equivalent of creating a hash of the password that’s sent over the wire instead of the actual password. But even those techniques didn’t solve the problem of the server securing the password, or a secure hash of the password. Or, for that matter, keeping you safe from replay attacks. Increasingly complex versions of this protocol were created, to the point where you could, with some degree of confidence, say that you were safe from man-in-the-middle attacks or replay attacks.

Users created a simple, easy to remember password, and brute force techniques guessed those passwords. So we came up with complex requirements for passwords, such as your password must contain an upper case, lower case, special character, and minimum length – and yet people still picked poor passwords. When they didn’t pick poor passwords that were easy to remember, they would reuse passwords across different systems. Or they would use password managers to store their passwords, until the password manager itself got compromised.

But even then, you’re not safe from passwords being leaked. Worse, leaked passwords are not detected – you don’t know if your password has been leaked until the leak is discovered. And these leaks could occur on a poorly implemented service. This means, no matter what you do, you’re still insecure.

Don’t Despair

There are solutions. There are concepts like MFA or one-time passwords that can be used in addition to your usual password. This is what you’ve experienced when you enter a credential, but in addition, you have to enter a code sent to you via SMS or from an authenticator app on your phone.

MFA and one-time passwords are great. In fact, I’d go to the extent of saying that if there’s a service you’re using that uses only username password, just assume it’s insecure, and don’t use it for anything critical. Additionally, pair it with common-sense practices like own your domain name, and a separate email address from your normal use email address for account recovery. Secret questions and answers that aren’t easy to guess, and answers that don’t make sense to anyone.

As great as MFA and one-time passwords are, they’re still not a perfect picture. There are a few big issues with this approach.

First, they are cumbersome to manage for the end user. I work with this stuff on a daily basis, and I find it frustrating to manage 100s of accounts, multiple authenticator apps, and I worry that if I ever broke my phone accidentally, I’d be transported to neanderthal times immediately. I can’t imagine how a common non-technology-friendly person deals with all this.

Second, MFAs and one-time passwords are both cumbersome and expensive for the service provider. All those SMS messages and push notifications cost money. This creates a barrier to entry for someone trying to get a service off the ground. Then there’s the question of which authenticator app to trust and whether that app be trusted. Is SMS good enough?

Third, there’s the issue of phishing. As great as MFA is, someone can set up a service that looks identical to a legit service, and unless you have very keen eyes watching every step, you may fall for it. Unfortunately, even the best of us is tired and stressed at times, and that’s when you fall for this. In fact, the unscrupulous service that pretends to be a legit service could simply forward your requests to the legit service after authentication while stealing your session. So you may think everything is hunky dory but your session has effectively been stolen.

Finally, there is authentication fatigue. Hey, I just want to login and use a system. Zero trust dictates that you assume a breach, so it’s common for services to over-authenticate. This creates authentication fatigue, and an already fatigued user could blindly approve an MFA request, especially if it’s cleverly disguised. It only takes one mistake for a hacker to get in the house, then they can do plenty of damage, potentially remaining undetected for a long time.

What am I Trying to Solve?

I’m not trying to secure passwords or make a better MFA solution here. The fundamental problem I wish to solve here is how an application can securely trust a user’s identity, such that the identity is not cumbersome to manage, is secure, convenient, and…

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How to re-generate Azure QR Code

Log in to Azure portal -> Active Directory -> Users.

Add user phone under Authentication contact info. Click on “Require re-register multifactor authentication. Reset password. Send email to user to login here ;

https://azure.microsoft.com/en-us/features/azure-portal/

User will be able to change the temp password. Next step will be the wizard that will re-register multifactor authentication on user phone in Microsoft Authentication App.

Windows security settings

Instructions to setup screen saver and strengthen the password;

Screensaver Settings

  1. Open your start menu and search for Change Screen Saver
  • Set the screen saver to blank, set the time to 15, and tick the box next to On resume, display login screen. Apply the settings. Your computer will now lock the screen after 15 minutes of inactivity.

Password Settings

  1. Open your start menu and search for Edit group policy.
  • In the left pane navigate to Computer Configuration/Windows Settings/Security Settings/Account Policies/Password Policy
  • Double click on each policy listed below to open the menu. Change the policy to match what is listed below. Apply the change and close the window.
    • Enforce password history: 12 passwords remembered
    • Maximum password age: 90 days
    • Minimum password age: 1 day
    • Minimum password length: 12 characters
    • Password must meet complexity requirements: Enabled
  • Open a file explorer window. Right-click on This PC and choose Manage
  • In the left pane, navigate to System Tools/Local Users and Groups/Users
  • Find your account in the list of users. Double click your account to open the settings menu
  • In the list of settings, make sure Password never expires is NOT checked. If it is, remove the check and Apply the changes.
  • Hit CTRL+ALT+DEL to bring up the system menu. Choose Change a password to change your password to a new one that meets the requirements.

Protected web api configuration

Like web apps, the ASP.NET and ASP.NET Core web APIs are protected because their controller actions are prefixed with the [Authorize] attribute. The controller actions can be called only if the API is called with an authorized identity.

Consider the following questions:

  • Only an app can call a web API. How does the API know the identity of the app that calls it?
  • If the app calls the API on behalf of a user, what’s the user’s identity?

Read more here;

https://docs.microsoft.com/en-us/azure/active-directory/develop/scenario-protected-web-api-app-configuration