Pre-Authentication Authorization

G5 Cyber Security

1 week ago

TL;DR

You generally shouldn’t implement authorization *before* authentication. Authentication verifies who the user is, while authorization determines what they can do. Trying to authorize before knowing who a user is creates security risks and complexity. Focus on authenticating first, then applying authorization rules.

Why It’s Usually Wrong

Authorization relies on identity. Without knowing the user’s identity (established through authentication), you have no basis for deciding what access they should be granted. Here’s why pre-authentication authorization is problematic:

Security Risks: You might grant access to someone pretending to be a different user, or allow anonymous users privileges they shouldn’t have.
Complexity: You need workarounds (like temporary tokens) that add significant overhead and potential vulnerabilities.
Broken Principles: It violates the fundamental security principle of least privilege – you’re giving access before verifying identity.

The Correct Order: Authentication First

Here’s the standard, secure approach:

Authentication: Verify the user’s identity (e.g., username/password, multi-factor authentication).
Authorization: Once authenticated, determine what resources and actions the user is allowed to access based on their role or permissions.

Common Scenarios & Solutions

Let’s look at some situations where people might *think* they need pre-authentication authorization and how to handle them correctly.

1. Rate Limiting

You want to limit the number of requests from a single source (IP address) to prevent abuse. This isn’t authorization; it’s a security measure applied before authentication, based on network characteristics, not user identity.

Solution: Implement rate limiting at the load balancer or web server level.

# Example Nginx rate limiting configuration

limit_req_zone $binary_remote_addr zone=mylimit:10m rate=5r/s;

server {

  location /api/ {

    limit_req zone=mylimit burst=10 nodelay;

...

2. Conditional Access Based on IP Address

You want to allow access only from specific office IPs. This is still not authorization in the traditional sense, but a network-level restriction.

Solution: Configure your firewall or web server to block/allow traffic based on source IP addresses.

# Example Apache configuration (using .htaccess)

Require ip 192.168.1.0/24

Allow from 10.0.0.0/8

3. Pre-Flight Checks (e.g., API Availability)

You want to check if an API endpoint is available before requiring authentication.

Solution: Create a simple, unauthenticated endpoint that returns the API status. This doesn’t grant access; it just indicates availability.

4. Captchas

You want to prevent bots from accessing your site.

Solution: Use CAPTCHAs before presenting a login form, but this is about preventing automated access, not authorizing users. It’s part of authentication (challenging the user to prove they are human).

In Summary

Focus on these steps:

Implement robust Authentication: Use strong passwords, multi-factor authentication, and secure protocols.
Define clear Authorization rules: Based on user roles or permissions.
Apply authorization *after* successful authentication.