# CORS Since v2.3.0

# Introduction

CORS, or "Cross-Origin Resource Sharing (opens new window)" is a mechanism that uses additional HTTP headers to tell browsers to give a web application running at one origin, access to selected resources from a different origin. A web application executes a cross-origin HTTP request when it requests a resource that has a different origin (domain, protocol, or port) from its own. Enabling CORS is done by adding a set of specific headers allowing the browser and server to communicate about which requests, methods and headers are or are not allowed. CORS support also comes with pre-flight OPTIONS requests support.

Most of the time, the API is using another domain as the clients. For security reasons, browsers restrict cross-origin HTTP requests initiated from scripts. That's why you should configure CORS for your API.

# Enabling CORS

All functions below require the cors package to be imported.

import "github.com/System-Glitch/goyave/v3/cors"

CORS options are set on routers. If the passed options are not nil, the CORS core middleware is automatically added.

router.CORS(cors.Default())

CORS options should be defined before middleware and route definition. All of this router's sub-routers inherit CORS options by default. If you want to remove the options from a sub-router, or use different ones, simply create another cors.Options object and assign it.

router.CORS(cors.Default())

subrouter := router.Subrouter("/products")
subrouter.CORS(nil) // Remove CORS options

options := cors.Default()
options.AllowCredentials = true
subrouter.CORS(options) // Different CORS options

TIP

All routes defined in a router having CORS options will match the OPTIONS HTTP method to allow pre-flight requests, even if it's not explicitly told in the route definition.

# Options

cors.Default() can be used as a starting point for custom configuration.

options := cors.Default()
options.AllowedOrigins = []string{"https://google.com", "https://images.google.com"}
router.CORS(options)

Find the options reference below:

# AllowOrigins

A list of origins a cross-domain request can be executed from. If the first value in the slice is * or if the slice is empty, all origins will be allowed.

Type: []string
Default: ["*"]

# AllowedMethods

A list of methods the client is allowed to use with cross-domain requests.

Type: []string
Default: ["HEAD", "GET", "POST", "PUT", "PATCH", "DELETE"]

# AllowedHeaders

A list of non simple headers the client is allowed to use with cross-domain requests. If the first value in the slice is *, all headers will be allowed. If the slice is empty, the request's headers will be reflected.

Type: []string
Default: ["Origin", "Accept", "Content-Type", "X-Requested-With", "Authorization"]

# ExposedHeaders

Indicates which headers are safe to expose to the API of a CORS API specification.

Type: []string
Default: []

# MaxAge

Indicates how long the results of a preflight request can be cached.

Type: time.Duration
Default: 12 hours (43200 seconds)

# AllowCredentials

Indicates whether the request can include user credentials like cookies, HTTP authentication or client side SSL certificates.

Type: bool
Default: false

# OptionsPassthrough

Instructs pre-flight to let other potential next handlers to process the OPTIONS method. Turn this on if your application handles OPTIONS.

Type: bool
Default: false