Document updated on Jun 27, 2024

API Key Authentication in KrakenD

API key authentication enables a Role-Based Access Control (RBAC) and a rate-limiting mechanism based on an API key passed by the client. For the desired endpoints, KrakenD rejects requests from users who do not provide a valid key, users trying to access a resource with insufficient permissions for their role, or exceeding the defined quota.

The authentication is granular and works per endpoint, meaning you can combine public endpoints (no API Key needed) and private endpoints in the same configuration.

The API Key component requires you to declare at least two different blocks of configuration:

1. The declaration of all known users and roles, placed at the root’s extra_config middleware section.
2. The association of which endpoints are protected, placed at each endpoint.

Declaring API Key users and roles

The first block of configuration declares how KrakenD retrieves keys, which ones are available, and the roles recognized by the system. It requires at least the keys attribute with a list of objects declaring each client’s key and roles. It looks like this:

{
  "version": 3,
  "extra_config": {
    "auth/api-keys": {
      "strategy": "header",
      "identifier": "Authorization",
      "keys": [
        {
          "key": "4d2c61e1-34c4-e96c-9456-15bd983c5019",
          "roles": ["role1", "role2"],
          "@description": "ACME Inc."
        },
        {
          "key": "58427514-be32-0b52-b7c6-d01fada30497",
          "roles": ["role1","role3"],
          "@description": "Administrators Inc."
        }
      ]
    }
  }
}

The configuration above is a simple implementation that stores API keys in plain text.

The list of possible configuration attributes is as follows:

It is also shown in the example a @description attribute to help you identify who this key belongs to. This attribute is metadata and unneeded by KrakenD, but it eases the administration of keys. Use keys starting with @ to place comments in the file.

Saving API keys hashed

When you declare the API keys in the list, if you don’t declare a hashing function, you write the key you want to pass when consuming endpoints as is.

When you declare a hash function (other than the default plain text), you must write the API key in the configuration after hashing it with the corresponding algorithm. These are the supported hashing functions:

• plain: No hashing. Key saved in plain text.
• fnv128: Hash the key using the non-cryptographic function 128-bit FNV-1.
• sha256: Hash the key using SHA256 (RFC6234)
• sha1: Hash the key using SHA1 (RFC3174)

In addition, you can pass a salt string, which will be prepended to the API key when resolving an API key:

string_to_hash = salt + api_key

Example: Saving API keys hashed with SHA256

Let’s say you want to give a user the API key abc. To hash the key, you can add a salt string, like mySalt, to spice up the output hash. Then you could type in a terminal:

$echo -n "mysaltabc" | sha256sum
2ad27678dd4fdf811ffe7f9c77801ab66e2cc62d08abb393451ddda48c1eba3f  -

Mac users might need to replace sha256sum with shasum -a 256. Then, the configuration needs to know the salt you chose to hash the key, and which hash function, so the gateway can produce the same output. It would look like this:

{
  "version": 3,
  "$schema": "https://www.krakend.io/schema/krakend.json",
  "debug_endpoint": true,
  "extra_config": {
    "auth/api-keys": {
      "salt": "mySalt",
      "hash": "sha256",
      "keys": [
        {
          "@description": "ACME Inc.",
          "key": "2ad27678dd4fdf811ffe7f9c77801ab66e2cc62d08abb393451ddda48c1eba3f",
          "@example": "echo -n 'mySaltabc' | sha256sum",
          "roles": [
            "user",
            "whitelabel"
          ]
        }
      ]
    }
  },
  "endpoints": [
    {
      "endpoint": "/foo",
      "backend": [
        {
          "url_pattern": "/__debug/user",
          "host": [
            "http://localhost:8080"
          ]
        }
      ],
      "extra_config": {
        "auth/api-keys": {
          "roles": [
            "user"
          ]
        }
      }
    }
  ]
}

Notice that the key in the configuration is the hashed value, not the API key. A leakage of the KrakenD configuration would not reveal the original API key abc that allows connecting to the endpoint.

Example: Saving API keys hashed with FNV-1

Here is another example with a small script in Go that generates the hash of an API key with a given salt in FNV-1 (test it online here):

package main

import (
  "fmt"
  "hash/fnv"
)

func main() {
  hash := fnv.New128()
  api_key := "4d2c61e1-34c4-e96c-9456-15bd983c5019"
  salt := "mySalt"
  hash.Write([]byte(salt + api_key))
  fmt.Printf("%x", hash.Sum(nil))
}

The configuration for this case would be as follows:

{
  "auth/api-keys": {
    "strategy": "header",
    "identifier": "X-Key",
    "hash": "fnv128",
    "salt": "mySalt",
    "@hashed-with": "https://go.dev/play/p/hHksLLCUJy3",
    "keys": [
        {
            "@key-plain": "4d2c61e1-34c4-e96c-9456-15bd983c5019",
            "key": "e0f7fce642685956791e58b835e26786",
            "roles": [
                "admin"
            ],
            "@description": "ACME Inc."
        }
    ]
  }
}

Protecting endpoints by API Key

Now that all users and roles are declared, it’s time to reference them in the endpoints. You must include the namespace auth/api-keys in its extra_config for all the endpoints needing API Key validation. Any endpoints not having the namespace are not API Key protected. For example, the endpoints could look like this:

{
  "endpoint": "/admin",
  "backend": [
    {
      "url_pattern": "/__debug/admin",
      "host": [
        "http://localhost:8080"
      ]
    }
  ],
  "extra_config": {
    "auth/api-keys": {
      "roles": [
        "admin"
      ],
      "client_max_rate": 5
    }
  }
}

The endpoint configuration accepts the following parameters:

Here is a full example of two different API Keys that can access three different endpoints:

{
  "version": 3,
  "extra_config": {
    "auth/api-keys": {
      "keys": [
        {
          "@description": "ACME Inc.",
          "key": "4d2c61e1-34c4-e96c-9456-15bd983c5019",
          "roles": ["user", "whitelabel"]
        },
        {
          "@description": "Administrators Inc.",
          "key": "58427514-be32-0b52-b7c6-d01fada30497",
          "roles": ["admin", "user"]
        }
      ]
    }
  },
  "endpoints": [
    {
      "endpoint": "/public",
      "backend": [
        {
          "url_pattern": "/__debug/public",
          "host": [
            "http://localhost:8080"
          ]
        }
      ]
    },
    {
      "endpoint": "/admin",
      "backend": [
        {
          "url_pattern": "/__debug/admin",
          "host": [
            "http://localhost:8080"
          ]
        }
      ],
      "extra_config": {
        "auth/api-keys": {
          "roles": [
            "admin"
          ],
          "client_max_rate": 5
        }
      }
    },
    {
      "endpoint": "/user",
      "backend": [
        {
          "url_pattern": "/__debug/user",
          "host": [
            "http://localhost:8080"
          ]
        }
      ],
      "extra_config": {
        "auth/api-keys": {
          "roles": [
            "user"
          ]
        }
      }
    }
  ]
}

Authenticating requests using API Key

When you don’t set any strategy in the configuration clients or use the header strategy, clients need to make requests to KrakenD adding the Authorization: Bearer or Authorization: Basic, but if you pass neither, the API Key is the whole content of the header value. Therefore, the value inside the header must strictly match the API key defined in the configuration after applying the selected procedure. See below.

Using Bearer

The format of the header is as follows:

Authorization: Bearer YOUR-KEY

For instance, having declared in the configuration a key 4d2c61e1-34c4-e96c-9456-15bd983c5019 that should be capable of seeing /foo, you should make a call like this:

$curl -H'Authorization: Bearer 4d2c61e1-34c4-e96c-9456-15bd983c5019' http://localhost:8080/foo
{"message":"pong"}

You write the API key after the bearer precisely as declared.

Using Basic authentication instead of Bearer

Another way of authenticating is using Basic authentication. However, it does not present any benefit compared to Bearer other than backward compatibility with legacy implementations.

The difference is that clients must pass the key in base64:

Authorization: Basic base64(YOUR-KEY:)

Notice that the encoding of the key contains an ending :. The final colon prevents your client from being asked for a password.

Basic authentication example

Repeating the previous Bearer example, let’s connect using Basic authentication now. The first step is to base64-encode:

$echo -n "4d2c61e1-34c4-e96c-9456-15bd983c5019:" | base64
NGQyYzYxZTEtMzRjNC1lOTZjLTk0NTYtMTViZDk4M2M1MDE5Ogo=

And then pass the header:

$curl -H"Authorization: Basic NGQyYzYxZTEtMzRjNC1lOTZjLTk0NTYtMTViZDk4M2M1MDE5Ogo=" http://localhost:8080/foo
{"message":"pong"}

You can also not do the base64 encoding if you use a client with regular basic auth implemented, which will encode automatically (again, notice the : at the end of the key):

$curl -i --user 4d2c61e1-34c4-e96c-9456-15bd983c5019: http://localhost:8080/foo
{"message":"pong"}

In case you forget the colon : you’ll be prompted for the password (when there isn’t):

$curl -i --user 4d2c61e1-34c4-e96c-9456-15bd983c5019 http://localhost:8080/user
Enter host password for user '4d2c61e1-34c4-e96c-9456-15bd983c5019':
HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
X-Krakend: Version
X-Krakend-Completed: true
Date: Tue, 10 Nov 2020 17:37:09 GMT
Content-Length: 18

{"message":"pong"}

Using an API key directly as a value

Another way of authenticating is passing the API Key directly in a header, without the Basic or the Bearer. When this happens, the full value of the header is used as API key.

For instance, when your clients call the gateway as follows:

$curl -H'x-api-key: 4d2c61e1-34c4-e96c-9456-15bd983c5019' http://localhost:8080/foo
{"message":"pong"}

You must set an identifier such as X-Api-Key.

Using a custom Authorization header

You can replace Authorization with any other header using the identifier option. But in all cases, the Bearer, the Basic, or no prefix are evaluated as described above.

For instance:

{
  "auth/api-keys": {
    "strategy": "header",
    "identifier": "X-Key"
  }
}

Clients will need to make calls like

$curl -H'X-Key: Bearer 4d2c61e1-34c4-e96c-9456-15bd983c5019' http://localhost:8080/foo
{"message":"pong"}

Or

$curl -H'X-Key: 4d2c61e1-34c4-e96c-9456-15bd983c5019' http://localhost:8080/foo
{"message":"pong"}

Passing the API key using a query string

If you set the strategy to query_string, clients can directly pass the key on the URL using ’ ?key=xxxx`. For instance:

$curl http://localhost:8080/user?key=4d2c61e1-34c4-e96c-9456-15bd983c5019
{"message":"pong"}

You can set a different identifier section instead of key to something else. For instance, let’s use ?mycustomapikey=xxxx:

{
  "auth/api-keys": {
    "strategy": "query_string",
    "identifier": "mycustomapikey",
    "keys": [{}]
  }
}

A configuration like the above will require users to make calls like this:

$curl http://localhost:8080/user?mycustomapikey=4d2c61e1-34c4-e96c-9456-15bd983c5019
{"message":"pong"}

Complete API Key configuration example

The following configuration snippet is fully functional. Run KrakenD with the debug flag (krakend run -d) to test it locally, as it uses itself as a backend. Explanation below:

{
    "version": 3,
    "extra_config": {
        "auth/api-keys": {
            "strategy": "header",
            "identifier": "Authorization",
            "propagate_role": "X-Krakend-Role",
            "keys": [
                {
                    "@description": "ACME Inc.",
                    "key": "4d2c61e1-34c4-e96c-9456-15bd983c5019",
                    "roles": [
                        "user",
                        "whitelabel"
                    ]
                },
                {
                    "@description": "Administrators Inc.",
                    "key": "58427514-be32-0b52-b7c6-d01fada30497",
                    "roles": [
                        "admin",
                        "user"
                    ]
                }
            ]
        }
    },
    "endpoints": [
        {
            "endpoint": "/public",
            "backend": [
                {
                    "url_pattern": "/__debug/public",
                    "host": [
                        "http://localhost:8080"
                    ]
                }
            ]
        },
        {
            "endpoint": "/admin",
            "backend": [
                {
                    "url_pattern": "/__debug/admin",
                    "host": [
                        "http://localhost:8080"
                    ]
                }
            ],
            "extra_config": {
                "auth/api-keys": {
                    "roles": [
                        "admin"
                    ]
                }
            }
        },
        {
            "endpoint": "/user",
            "backend": [
                {
                    "url_pattern": "/__debug/user",
                    "host": [
                        "http://localhost:8080"
                    ]
                }
            ],
            "extra_config": {
                "auth/api-keys": {
                    "roles": [
                        "user"
                    ]
                }
            }
        },
        {
            "endpoint": "/custom-header",
            "backend": [
                {
                    "url_pattern": "/__debug/custom-header",
                    "host": [
                        "http://localhost:8080"
                    ]
                }
            ],
            "extra_config": {
                "auth/api-keys": {
                    "roles": [
                        "admin"
                    ],
                    "@comment": "Instead of the Authorization header, we will use X-ADMIN-KEY",
                    "identifier": "X-User-Key",
                    "strategy": "header"
                }
            }
        }
    ]
}

In this example, we have enabled two different API users. One with key 4d2c61e1-34c4-e96c-9456-15bd983c5019 (let’s say a customer of ACME Inc.) and another one with the key 58427514-be32-0b52-b7c6-d01fada30497 (an administrator of my company).

Both users share the role users, and they can access all the protected endpoints as this role is included. Nevertheless, the /admin endpoint is reachable by the administrator only, as the role “admin” is required. The backend also receives a header X-Krakend-Role with the matching role.

The endpoint /public is always accessible, with or without the Authorization header, as it does not include the API key middleware configuration.

Finally, all endpoints expected the Authorization header, but in the endpoint /custom-header, we decided to use a different one and override it for this endpoint only. Therefore, we will use the X-User-Key header instead.

And now some sample interactions:

$curl -H'Authorization: Bearer 4d2c61e1-34c4-e96c-9456-15bd983c5019' http://localhost:8080/user
{"message":"pong"}

$curl -i --user 4d2c61e1-34c4-e96c-9456-15bd983c5019: http://localhost:8080/user
HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
X-Krakend: Version
X-Krakend-Completed: true
Date: Tue, 10 Nov 2020 17:07:46 GMT
Content-Length: 18

{"message":"pong"}

$curl -iG -H'Authorization: Bearer 4d2c61e1-34c4-e96c-9456-15bd983c5019' http://localhost:8080/admin

HTTP/1.1 401 Unauthorized
Date: Tue, 10 Nov 2020 17:01:03 GMT
Content-Length: 0

$curl -iG -H'Authorization: Bearer INVALID-API-KEY' http://localhost:8080/user

HTTP/1.1 401 Unauthorized
Date: Tue, 10 Nov 2020 16:59:35 GMT
Content-Length: 0

$curl http://localhost:8080/public
{"message":"pong"}

$curl -iG -H'X-User-Key: Bearer 4d2c61e1-34c4-e96c-9456-15bd983c5019' http://localhost:8080/custom-header
{"message":"pong"}

Rate limiting usage of API Keys

The attribute client_max_rate allows you to set the maximum requests per second you allow in an endpoint or in the service. The rate limit you set is the same for all the API Keys. For instance, given the following endpoint configuration:

{
  "endpoint": "/members",
  "backend": [
    {
      "url_pattern": "/api/v1/members"
    }
  ],
  "extra_config": {
    "auth/api-keys": {
      "roles": [
        "admin",
        "user"
      ],
      "client_max_rate": 5
    }
  }
}

With this configuration, API Keys are limited to 5 requests per second. But what if you wanted to set different limits for the admin and the user role? In that case you can use instead the rate limiting based on tiers and remove the client_max_rate from this configuration.

Onboard new API key customers without restarts

As the KrakenD configuration is static and only changes once you restart the process or you do a deployment, you might find it inconvenient to onboard new customers with new API keys. The following advice can be handy.

Create a pool of available API keys instead of waiting for user registration in your system to insert a new API key. KrakenD has stable performance; it doesn’t change if you have 100 keys or 1 million.

An easy way to generate API keys could be as follows:

$uuidgen

If you want to generate several keys and write part of the configuration file, you could use something like:

$for i in $(seq 50)
do
  key=$(uuidgen)
  echo "{ \"key\": \"$key\", \"roles\": [\"silver-plan\"], \"@status\": \"free\" },"
done

Then you would use the output above to create a partial file api-keys.json that would be used on KrakenD with Flexible Configuration.

Finally, your backend should have this list somewhere, and when a new user registers, you assign one of the free keys to the new user. You can deploy from time to time when you are running out of API keys in the pool or if you want to write the assignment in the configuration.