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Building a Backend Application with Go

Middleware Creation for REST API

Learn how to add middleware to the REST API application.

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Add middleware

Middleware is a component that acts as an interceptor for the request before another request has proceeded. For example, the middleware is added to create a new item request. In this example, the middleware acts as authentication to ensure the authenticated user can create a new item request.

Inside the auth.go file in the utils directory, we add some helpers for authentication purposes.

Before the GenerateNewAccessToken() function, we add a struct for storing the JWT token’s metadata.

type TokenMetadata struct {
	Expires int64
}

After the GenerateNewAccessToken() function, we create a helper function called ExtractTokenMetadata.

Go (1.18.2)
// ExtractTokenMetadata returns token metadata
func ExtractTokenMetadata(c *fiber.Ctx) (*TokenMetadata, error) {
	// verify the token
	token, err := verifyToken(c)
	// if verification is failed, return an error
	if err != nil {
		return nil, err
	}
	// get the token claim data
	claims, ok := token.Claims.(jwt.MapClaims)
	//  if token claim data exists and token is valid
	if ok && token.Valid {
		// set the token expiration date
		expires := int64(claims["exp"].(float64))
		// return the token metadata
		return &TokenMetadata{
			Expires: expires,
		}, nil
	}
	// return an error if token is invalid
	return nil, err
}
Function to create token metadata from the valid JWT token

In the code above, the ExtractTokenMetadata() function is used to extract the token metadata.

We then create a function called CheckToken ...