Security

Security-related documentation in Swagger is described in Security Definitions Object and Security Requirement Object

Standard Swagger features in combination with some extensions can be used to configure security checks about JWT tokens which are expected to be sent with a client request. If the JWT token is valid, it is stored in a variable, which can then be used in the flow.

The x-flat-jwt field

The x-flat-jwt field references an object with fields describing the expected JWT token:

  • key - REQUIRED. The key to decode the JSON Web Signature (JWS). This can either be specified with a value, or by referencing a file (file) or an environment variable (env).

  • alg - The signing algorithm the JWS is expected to be created with. This can either be specified with a value, or by referencing a file (file) or an environment variable (env). See the algorithm parameter for jwt-decode() for more information.

  • out-var - The name of the variable in which the JWT is stored (must be a proper variable name, starting with $; default: "$jwt").

  • out-header - The name of an HTTP request header that shall carry the JWT in upstream requests.

  • claims - An object with claims the JWT payload is expected to contain. The field names are the claim names, the expected claim value is specified either with a value, or by referencing a file (file) or an environment variable (env).

  • scope-claim - The name of the claim, storing the scope of the token (string; default: scope). The claim value must either be

    • a string containing a whitespace-separated list of scopes ("scope1 scope2 scope3") or

    • an array with a string entry for each scope (["scope1", "scope2", "scope3"]).

  • post-check-flow - The path to a flow executed after the JWT is checked and found valid. In this flow, e.g. additional checks can be implemented (use the error action to throw errors).

The token is considered valid if all of the following are true:

  • the JWS can be decoded,

  • the JWS has a proper JWT,

  • the JWT is not expired,

  • the JWT contains the expected claims, if any are configured,

  • the scope of the token contains all required scopes as specified in the security requirement,

  • the JWT can be stored in a variable.

$jwt or the alternative variable specified in out-var and the header specified in out-header will be unset if the token is not valid.

JWT in Authorization Header

Use a Security Scheme Object with type: apiKey, in: header and name: Authorization if the JWT is expected to be sent as a bearer token in an Authorization header; e.g.:

securityDefinitions:
JWTHeaderAuth:
type: apiKey
in: header
name: Authorization
x-flat-jwt:
key:
file: secret.pem
alg:
env: FLAT_JWT_ALG
out-var: $header_token
scope-claim: permission
claims:
aud:
env: FLAT_JWT_AUDIENCE

The code in this example defines a security scheme named JWTHeaderAuth. The token is expected to be a bearer token in the Authorization header. The key is read from a file named secret.pem relative to the swagger.yaml. The signing algorithm is read from the FLAT_JWT_ALG environment variable. The JWT will be stored in the $header_token variable. The scope of the token is specified in a permission claim. The JWT payload is expected to contain an aud claim with a value read from the FLAT_JWT_AUDIENCE environment variable.

If the request does not contain an Authorization header with the proper bearer structure, or the token is invalid, this security scheme will fail.

JWT in Cookie

Use a Security Scheme Object with type: apiKey, in: header, name: Cookie and x-flat-cookiename: <name> if the JWT is expected to be sent as a cookie value; e.g.:

securityDefinitions:
JWTCookieAuth:
type: apiKey
in: header
name: Cookie
x-flat-cookiename: authtoken
x-flat-jwt:
key:
env: FLAT_COOKIE_SECRET
out-var: $cookie_token

In this example the key is read from the FLAT_COOKIE_SECRET environment variable. The JWT signing algorithm is unspecified – it defaults to HS256. The JWT will be stored in $cookie_token. No claims are expected.

If the request does not contain a Cookie header with an authtoken cookie, or the token is invalid, this security scheme will fail.

Security Scheme Combinations

Swagger allows for combinations of security schemes to be applied to API endpoints. If security schemes are specified as alternatives, at least one alternative must not fail. In the following example, a GET request to /foo must satisfy at least one of the security schemes named JWTHeaderAuth and JWTCookieAuth.

paths:
/foo:
get:
security:
- JWTHeaderAuth: []
- JWTCookieAuth: []

Applying Security Schemes

In Swagger, security schemes can be specified at the top level (default security) or for specific operations. With FLAT, you can also specify a security scheme for a specific path (default security for all operations on the path).

In the following example, a GET request to /foo must satisfy the security scheme named JWTHeaderAuth, a POST request to /foo must satisfy the security scheme named JWTHeaderAuth and the token must have both write:foo and read:bar scopes, while e.g. a DELETE or PUT request to /foo must satisfy the security scheme named JWTCookieAuth. All other requests must satisfy either the JWTHeaderAuth or JWTCookieAuth security schemes.

Note: While in Swagger 2.0, specifying scopes in security requirements is limited to OAuth2 security definitions, FLAT has no such limitation.

# default
security:
- JWTHeaderAuth: []
- JWTCookieAuth: []
paths:
/foo:
# default for all operations on /foo
security:
- JWTCookieAuth: []
get:
# specific for GET on /foo
security:
- JWTHeaderAuth: []
post:
# specific for POST on /foo
security:
- JWTHeaderAuth: [ write:foo, read:bar ]

If a request does not pass the security check, it is rejected with status code 403 and error code 3206, and the error flow is run, if configured.

The security check is performed after validation.

Full Example

securityDefinitions:
JWTHeaderAuth:
type: apiKey
in: header
name: Authorization
x-flat-jwt:
key:
file: secret.pem
alg:
env: FLAT_JWT_ALG
out-var: $header_token
scope-claim: permission
claims:
aud:
env: FLAT_JWT_AUDIENCE
JWTCookieAuth:
type: apiKey
in: header
name: Cookie
x-flat-cookiename: authtoken
x-flat-jwt:
key:
env: FLAT_COOKIE_SECRET
out-var: $cookie_token
JWTCookieAuth2:
type: apiKey
in: header
name: Cookie
x-flat-cookiename: authtoken2
x-flat-jwt:
key:
env: FLAT_COOKIE_SECRET
out-var: $cookie_token2
post-check-flow: check-cookie-jwt.xml
security: # alternatives: token in Authorization header or authtoken cookie
- JWTHeaderAuth: []
- JWTCookieAuth: []
paths:
/: # default security as defined at top-level
/foo:
get:
security: # token must be in Authorization header
- JWTHeaderAuth: []
post:
# specific for POST on /foo
security:
- JWTHeaderAuth: [ write:foo, read:bar ]
/projects/{p}:
get:
security:
- JWTCookieAuth2: []
parameters:
- name: p
in: path
type: string
required: true

check-cookie-jwt.xml (checking whether the value of the pid JWT claim equals the p request path parameter):

<flow>
<log>
{
"token_id": {{ $cookie_token2/pid }},
"path_id": {{ $request/params/p }}
}
</log>
<error if="not($cookie_token2/pid) or $cookie_token2/pid != $request/params/p">
{
"status": 401,
"message": "Token is not applicable for this project."
}
</error>
</flow>

Forwarding JWT Upstream

The claims of an incoming JWT are stored in $jwt – or in the global variable that you specify in the out-var property of x-flat-jwt. In a request or proxy-request action you can send these claims upstream, for example using a query parameter or a header:

<flow>
<proxy-request>
{
"url": "https://httpbin.org/get",
"query": {{ $jwt }}, <!-- ⬅ as query parameters -->
"headers": {
"Token": {{ json-stringify($jwt) }} <!-- ⬅ as 'Token' header -->
}
}
</proxy-request>
</flow>

If we assume the value of $jwt being {"id":42,"name":"John Doe"}, the resulting upstream request URL would be https://httpbin.org/get?id=42&name=John%20Doe and the request would include a Token header: Token: {"id":42,"name":"John Doe"}.

To just forward the received JWT token upstream as a header, you can also specify the desired header name with the out-header property of x-flat-jwt:

securityDefinitions:
JWTHeaderAuth:
x-flat-jwt:
key:
out-header: Token # ⬅ forwards this JWT in the 'Token' header

The headers section in proxy-request is then no longer needed:

<flow>
<proxy-request>
{
"url": "https://httpbin.org/get"
}
</proxy-request>
</flow>

Moreover, if you just want to proxy requests, there's no need to define a flow and you can simply set up your requests using x-flat-proxy:

securityDefinitions:
JWTHeaderAuth:
x-flat-jwt:
key:
out-header: Token # ⬅ forwards the JWT in the 'Token' header
paths:
/:
get:
x-flat-proxy: # ⬅ no more x-flat-flow
url: https://httpbin.org/get
security:
- JWTHeaderAuth: []

See also