Just finished a security review. Here are the 5 Auth0 configs we fixed.

After completing our annual security audit, the Auth0 tenant configuration emerged as a significant area for remediation. While the platform is robust, its flexibility can lead to subtle misconfigurations that introduce risk. Our review focused on the principle of least privilege and tightening attack surfaces. Here are the five key items we corrected.

First, we overhauled our **Application Grant Types**. We discovered several machine-to-machine applications configured with the implicit grant, which returns tokens directly in the URL fragment. This is unsuitable for server-side workflows. We migrated these to the Client Credentials grant and ensured all web apps used the Authorization Code Flow with Proof Key for Code Exchange (PKCE). The change is straightforward in the Auth0 dashboard but critical for mitigating authorization code interception.

```json
// Auth0 Application Settings - What we enforced:
{
"grant_types": [
"authorization_code",
"refresh_token" // where appropriate
],
"callbacks": ["https://app.example.com/callback"],
"oidc_conformant": true
}
```

Second, we enforced **role-based access control (RBAC) with explicit API assignments**. We had previously assigned permissions to users via roles, but those roles were not explicitly linked to the target API in Auth0. This meant the `scope` claim in access tokens was often incorrect or missing. We configured each role's permissions to be associated with a specific API identifier, ensuring tokens contain valid, verifiable scopes.

Third, we disabled the **Auth0 Management API v1**. We were still using the legacy v1 endpoint for some automated scripts. v1 lacks the fine-grained access control of v2. We migrated all automation to use the v2 API, creating dedicated machine-to-machine applications with scopes limited strictly to the necessary management actions (e.g., `read:users`, `update:users_app_metadata`). This drastically reduced the potential blast radius of a compromised token.

Fourth, we reviewed and pruned **custom database connections and rules**. An old custom database connection for a deprecated service was still active and had overly permissive rules. We archived the connection and audited our remaining rules for potential security issues, such as overly verbose error logging or missing input sanitization. Each rule was evaluated for its necessity and current security posture.

Finally, we configured **brute force protection** at the tenant level, which was surprisingly not enabled. We set it to block IPs for an hour after 10 failed login attempts on a single account. While this seems basic, it was a default we had overlooked during initial setup. This provides a necessary layer of defense against credential stuffing, particularly on administrative accounts.

Each change was logged, tested in a development tenant, and rolled out during a maintenance window. The process highlighted the importance of treating identity infrastructure as code and subjecting it to regular, rigorous review.