## JWT 中間件
JWT 提供了一個 JSON Web Token (JWT) 認證中間件。
- 對于有效的 token，它將用戶置于上下文中并調用下一個處理程序。
- 對于無效的 token，它會發送 "401 - Unauthorized" 響應。
- 對于丟失或無效的 `Authorization` 標頭，它會發送 "400 - Bad Request" 。
*用法*
```go
e.Use(middleware.JWT([]byte("secret"))
```
### 自定義配置
*用法*
```go
e.Use(middleware.JWTWithConfig(middleware.JWTConfig{
SigningKey: []byte("secret"),
TokenLookup: "query:token",
}))
```
### 配置
```go
// JWTConfig defines the config for JWT middleware.
JWTConfig struct {
// Skipper defines a function to skip middleware.
Skipper Skipper
// Signing key to validate token.
// Required.
SigningKey interface{}
// Signing method, used to check token signing method.
// Optional. Default value HS256.
SigningMethod string
// Context key to store user information from the token into context.
// Optional. Default value "user".
ContextKey string
// Claims are extendable claims data defining token content.
// Optional. Default value jwt.MapClaims
Claims jwt.Claims
// TokenLookup is a string in the form of "<source>:<name>" that is used
// to extract token from the request.
// Optional. Default value "header:Authorization".
// Possible values:
// - "header:<name>"
// - "query:<name>"
// - "cookie:<name>"
TokenLookup string
// AuthScheme to be used in the Authorization header.
// Optional. Default value "Bearer".
AuthScheme string
}
```
*默認配置*
```go
DefaultJWTConfig = JWTConfig{
Skipper: defaultSkipper,
SigningMethod: AlgorithmHS256,
ContextKey: "user",
TokenLookup: "header:" + echo.HeaderAuthorization,
AuthScheme: "Bearer",
Claims: jwt.MapClaims{},
}
```
### [示例](https://echo.labstack.com/cookbook/jwt)
