Rate Limit Use Cases

There are a handful of ways to determine if a customer product is being rate limited by Auth0. See below for the possible causes of rate limitation.

You can use tenant logs for more information on request limits. The api_limit is exported in the logs immediately after a rate limit is exceeded for a specific rate limit bucket. If the rate limit is still being exceeded after an hour for that same rate limit bucket, then a second log is created. If a rate limit is exceeded for a different rate limit bucket, a new api_limit event is created.  This enables customers to determine which rate limit configuration their API calls are triggering, and is a critical first step to determining root cause.  

To learn more about tenant logs, read Logs.

Auth0 API responses deliver HTTP 429 (Too Many Requests) responses with the exceeded rate limit. This enables customers to observe rate limit enforcement in real time. However, this is only useful for custom-built customer applications interacting directly with the Auth0 API.

If you are using an SDK, refer to the Management API SDK libraries error pages.

The error page response is sent for endpoints that render HTML content to the end user. If your tenant is configured to use generic (Auth0 hosted) pages, Auth0 renders the error page instead of the expected content when you exceed the response limit.  If your tenant is configured to use custom error pages, the user is redirected to the custom error page URL with the relevant error in the error_description query string parameter.  For more information, see Affected endpoints and the JSON Error descriptions.

If you believe tenant requests are rate limited and need assistance to understand why, open a request via the Support Center.  As part of your request, please include the full raw log where the issue was seen.

Auth0 reports up-to-date information on the current status of your rate limits using HTTP response headers from endpoints that have rate limit policies configured. This status is communicated as follows:

• x-ratelimit-limit: Maximum number of requests available.

• x-ratelimit-remaining: Number of remaining requests available until the bucket is refilled with additional requests.

• x-ratelimit-reset: UNIX timestamp, in seconds, of the expected time when additional requests will be added to the bucket.

For example:

An API has the following rate limit:

• Burst Limit: 1000

• Sustained Rate Limit: 100 requests per second (on a fixed window)

From this information, you can derive:

• The sustained rate limit is 100 requests per second on a fixed window.

• Due to the fixed window, the bucket of requests is refilled every second.

If you receive the following x-headers in your API response:

• x-ratelimit-limit: 1000

• x-ratelimit-remaining: 50

• x-ratelimit-reset: 1675452600

You now know that:

• Your tenant has used up 950 of the 1000 requests allowable to that API, and only has 50 requests remaining until such time that additional requests are added.

• New requests will be added at 1675452600, or 7:30:00 PM UTC on February 3, 2023.

• 1 new request will be added at that time 

Therefore, if you are making requests at a rate greater than what is described above, then a rate limitation is expected.  How soon you will be rate limited depends on the burst limit and to what extent you are exceeding the sustained limit.

Assume Auth0 launches a new API called /ratelimitexample with the following rate limit values:

• Burst limit: Five (5) requests

• Sustained rate limit: 10 requests per second.

Key points:

• API begins with, and will never exceed, five request tokens, which is equal to the burst limit.

• The bucket of 10 tokens is refilled every second, using a “fixed window.” New tokens are added to the bucket, refilling the it at the “top” of each second.

 Example scenario with rate limits:  

In this scenario:

• T0 - T1sec:  The end user makes six requests in the first second.  Five requests – equal to the burst limit – receive a 200 response.  The sixth request receives a 429 error because there are no remaining request tokens in the bucket.

• T1sec - T2sec:  Auth0 tops off the bucket of request tokens because of the fixed window algorithm. As a result, the seventh through 11th requests are successful, exhausting the bucket by the 12th request, resulting in a 429 error.

• T2sec - T3sec:  Auth0 refills the token bucket once again, and the next request (13) receives a 200 response.

Assume Auth0 launches a new API called /ratelimitexample2 with the following rate limit values:

• Burst limit:  Five (5) requests

• Sustained Rate limit:  Six (6) requests per minute.

Key points:

• API begins with five request tokens, which is equal to the burst limit.

• The bucket of six tokens is refilled every minute, using a “fixed window.” New tokens are added to the bucket, refilling the it at the “top” of each minute.

Example scenario with rate limits:  

In this scenario:

• T0 - T+1min:  The end user makes six requests in the first minute. Five requests – equal to the burst limit – receive a 200 response.  The sixth request receives a 429 error because there are no remaining request tokens.

• T+1min - T+2min:  Auth0 refills the token bucket because of the fixed window algorithm. As a result, the seventh through 11th requests are successful, exhausting the bucket by the 12th request, resulting in a 429 error.

• T+2min: Auth0 refills the token bucket once again, and the next request (13) receives a 200 response.

On occasion, Auth0 will assign two rate limits to a single API.  This is done in order to configure a burst limit and the sustained rate limit that is more customized to the needs of the service.  In effect, the first rate limit becomes the effective burst limit, and the second rate limit becomes the effective sustained rate limit.  In this scenario, Auth0 only publishes the effective burst and sustained rate limits, rather than communicating the actual burst and sustained rate limits.

There are a handful of Authentication Flows, including Login, Signup and Change Password.  The most common of these are typically Login, followed by Signup.

An end user's login initiates multiple API calls to Authentication API endpoints in order to determine if the end user is authorized to receive an Authorization token, and thereby access the application they have requested.

The precise number of API calls is a function of a handful of configurations:

• Authentication Experience (e.g., New Universal Login or Classic Login)

• Authentication Flow (e.g., Login, Signup, or Change Password)

• Authentication Flow Type (e.g., Login via Username / Password; Login via Social Login; Login when an existing Authentication Token already exists)

Below, we describe some common customer configurations, and their impact on API Usage.

Auth0 Universal Login provides the essential feature of an authorization server: the login flow. When a user needs to prove their identity to gain access to your application, you can redirect them to Universal Login and let Auth0 handle the authentication process.

Classic Login is an Auth0-hosted login experience that relies on JavaScript for customization. Implementing Classic Login is less complex than embedding the authentication process directly in your app, and it can help prevent the dangers of cross-origin authentication.