By Marone: August 2020

Secure API behind
Spring Cloud Gateway with apikey

Spring Cloud Gateway apikey

Table of contents


Sometimes there a need to secure an API with API key. When I started looking for examples about how spring cloud gateway deal with apikey, I found some articles but no examples. So we decide to write this short article.

If it were up to me, I would always prefer OAuth2. But sometimes there are cases where the customer wants something easy and simple for authentication. Furthermore, there are many public APIs that use an apikey, such as Google Maps, Twitter,..etc. And I can tell you the list was long.

What is API Key?

An application programming interface key (API Key) is a unique piece of code used to authenticate the calling user, developer, or application.
Basically used to limit and monitor the usages of an API. The API keys are part of the request and therefore less secure. If you want to take a look at how the combination between API Gateway and OAuth2 works, here is an example of how KONG deals with it.

How to pass an apikey?

An API key can then be passed through: In the following example, we will use the request header way.

Used tools

Java 11
Maven 3.x
cURL 7.x

The custom Filter

Spring Cloud Gateway provides out of the box a lot of filters, but in this case we will write a custom filter. Custom filters have to implement the GatewayFilter and Ordered interfaces.

The getOrder() method is used to set the order of the filter. The filter method is part of GatewayFilter and mostly used to implement some cross-cutting logic. In our case it will check if the caller is allowed to consume the downstream service. This logic should be executed before the request passed. Generally speaking, we implemented a Prefilter.
In the example the filter is used to extract the apikey from header and check if is valid. If the apikey is not present or not match the dummy data the filter returns 401 status code.

Please keep in mind this example is made simple just to demonstrate how to secure an API with apikey and how powerful filters are.
The checkApikey(String routeId, String apikey) method is straightforward, here you can impelement some logic to get data from store and compare it with the given apikey. The custom filter can also read the name of the route routeId

Use the Filter

Now we need to register the ApiKeyFilter to the route

let's test

Curl command

When passing a appropriate apikey the request will be forwarded to
The Gatewayfilter extracts the header and checks if the consumer is allowed to call the downstream service. In this case, the authentication was successful and we got a response from

Curl command without apikey

Now testing without header, the api gateway respond with 401 Unauthorized


The complete code can be found in GitHub