带cookie跨域问题的思路以及echo的解决方案

问题起因

前后端分离，前端要访问后端资源，而且需要携带cookie信息,这时碰到了跨域问题。一开始以为设置为允许跨域allow_origins为即可。可是浏览器还是拦截的请求，于是查看跨域规则，原来跨域allow_origins为时，只允许简单的跨域，比如get,post，但是如果携带cookie，则会出现失败。

思路

后来查看文档，原来按照跨域请求的规则，当跨域和来源一致时才可以携带cookie。详情见阮一峰的博客

echo框架中的解决办法

有了思路就好办了，echo框架中的跨域设置不够详细，做不到设置来源跨域。于是我修改了一下其中的跨域中间件，增加了一子域名的跨域。

实际上可以修改为，任意来源的跨域，但是这样就不能保证安全了，不过如果是做接口平台倒是可以这么办。

完整代码为：

package echo_cors
import (
	"net/http"
	"strconv"
	"strings"
	"github.com/labstack/echo"
	"github.com/labstack/echo/middleware"
)
type (
	// CORSConfig defines the config for CORS middleware.
	CORSConfig struct {
		// Skipper defines a function to skip middleware.
		Skipper middleware.Skipper
		// AllowOrigin defines a list of origins that may access the resource.
		// Optional. Default value []string{"*"}.
		AllowOrigins []string `json:"allow_origins"`
		// AllowMethods defines a list methods allowed when accessing the resource.
		// This is used in response to a preflight request.
		// Optional. Default value DefaultCORSConfig.AllowMethods.
		AllowMethods []string `json:"allow_methods"`
		// AllowHeaders defines a list of request headers that can be used when
		// making the actual request. This in response to a preflight request.
		// Optional. Default value []string{}.
		AllowHeaders []string `json:"allow_headers"`
		// AllowCredentials indicates whether or not the response to the request
		// can be exposed when the credentials flag is true. When used as part of
		// a response to a preflight request, this indicates whether or not the
		// actual request can be made using credentials.
		// Optional. Default value false.
		AllowCredentials bool `json:"allow_credentials"`
		// ExposeHeaders defines a whitelist headers that clients are allowed to
		// access.
		// Optional. Default value []string{}.
		ExposeHeaders []string `json:"expose_headers"`
		// MaxAge indicates how long (in seconds) the results of a preflight request
		// can be cached.
		// Optional. Default value 0.
		MaxAge         int `json:"max_age"`
		AllowSubDomain bool
		MainDomain     string
		AllowAllHost   bool
	}
)
var (
	// DefaultCORSConfig is the default CORS middleware config.
	DefaultCORSConfig = CORSConfig{
		Skipper:      middleware.DefaultSkipper,
		AllowOrigins: []string{"*"},
		AllowMethods: []string{echo.GET, echo.HEAD, echo.PUT, echo.PATCH, echo.POST, echo.DELETE},
	}
)
// CORS returns a Cross-Origin Resource Sharing (CORS) middleware.
// See: https://developer.mozilla.org/en/docs/Web/HTTP/Access_control_CORS
func CORS() echo.MiddlewareFunc {
	return CORSWithConfig(DefaultCORSConfig)
}
// CORSWithConfig returns a CORS middleware with config.
// See: `CORS()`.
func CORSWithConfig(config CORSConfig) echo.MiddlewareFunc {
	// Defaults
	if config.Skipper == nil {
		config.Skipper = DefaultCORSConfig.Skipper
	}
	if len(config.AllowOrigins) == 0 {
		config.AllowOrigins = DefaultCORSConfig.AllowOrigins
	}
	if len(config.AllowMethods) == 0 {
		config.AllowMethods = DefaultCORSConfig.AllowMethods
	}
	allowMethods := strings.Join(config.AllowMethods, ",")
	allowHeaders := strings.Join(config.AllowHeaders, ",")
	exposeHeaders := strings.Join(config.ExposeHeaders, ",")
	maxAge := strconv.Itoa(config.MaxAge)
	return func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c echo.Context) error {
			if config.Skipper(c) {
				return next(c)
			}
			req := c.Request()
			res := c.Response()
			origin := req.Header.Get(echo.HeaderOrigin)
			allowOrigin := ""
			// Check allowed origins
			for _, o := range config.AllowOrigins {
				if o == "*" || o == origin {
					allowOrigin = o
					break
				}
			}
			if config.AllowSubDomain && config.MainDomain != "" {
				if strings.Contains(origin, config.MainDomain) {
					allowOrigin = origin
				}
			}
			if config.AllowAllHost {
				allowOrigin = c.Scheme()+"://"+req.Host
			}
			// Simple request
			if req.Method != echo.OPTIONS {
				res.Header().Add(echo.HeaderVary, echo.HeaderOrigin)
				res.Header().Set(echo.HeaderAccessControlAllowOrigin, allowOrigin)
				if config.AllowCredentials {
					res.Header().Set(echo.HeaderAccessControlAllowCredentials, "true")
				}
				if exposeHeaders != "" {
					res.Header().Set(echo.HeaderAccessControlExposeHeaders, exposeHeaders)
				}
				return next(c)
			}
			// Preflight request
			res.Header().Add(echo.HeaderVary, echo.HeaderOrigin)
			res.Header().Add(echo.HeaderVary, echo.HeaderAccessControlRequestMethod)
			res.Header().Add(echo.HeaderVary, echo.HeaderAccessControlRequestHeaders)
			res.Header().Set(echo.HeaderAccessControlAllowOrigin, allowOrigin)
			res.Header().Set(echo.HeaderAccessControlAllowMethods, allowMethods)
			if config.AllowCredentials {
				res.Header().Set(echo.HeaderAccessControlAllowCredentials, "true")
			}
			if allowHeaders != "" {
				res.Header().Set(echo.HeaderAccessControlAllowHeaders, allowHeaders)
			} else {
				h := req.Header.Get(echo.HeaderAccessControlRequestHeaders)
				if h != "" {
					res.Header().Set(echo.HeaderAccessControlAllowHeaders, h)
				}
			}
			if config.MaxAge > 0 {
				res.Header().Set(echo.HeaderAccessControlMaxAge, maxAge)
			}
			return c.NoContent(http.StatusNoContent)
		}
	}
}

用法

已经放到github了

这里增加了三个变量，AllowSubDomain，允许二级域名，MainDomain根域名，AllowAllHost 允许所有的跨域

• CORSWithConfig(CORSConfig{AllowCredentials:true,AllowSubDomain:true,MainDomain:"main.com"}) 允许子域名跨域
• CORSWithConfig(CORSConfig{AllowCredentials:true,AllowAllHost:true})
  
  对于js，也要做对应修改，axios的修改如下：

const Axios = axios.create({
    headers: {
        'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8'
    },
    withCredentials: true
});
Axios.interceptors.request.use(
    config => {
        if (config.method === 'post' || config.method === 'put') {
            if (config.data) {
                var queryString = Object.keys(config.data)
                    .map(key => {
                        return encodeURIComponent(key) + '=' + encodeURIComponent(config.data[key]);
                    })
                    .join('&');
                config.data = queryString;
            }
            return config;
        }
        return config;
    },
    error => {
        return Promise.reject(error);
    }
);