A Deep Dive into Secure Authentication 🛡️💻

A few months ago, I had the opportunity to co-present a tech talk titled “JWTs in Go: A Deep Dive into Secure Authentication” And honestly? It was one of those sessions where you walk away having learned just as much as you shared.

We explored the world of JSON Web Tokens (JWTs), their role in securing modern applications, and how to implement them effectively in Go.This article is a reflection of that session, peppered with lessons and some personal takeaways that stuck with me.

What Exactly Are JWTs?

JWTs are like digital passports they help two parties trust each other without constantly asking “Who are you again?” They consist of three parts:

Header.Payload.Signature

Header: Info about the token algorithm, token type.

Payload: The claims. Think user ID, roles, or anything relevant.

Signature: Ensures that no one tampered with the token.

They’re encoded (not encrypted!) and meant to be verified, not trusted blindly.

Why JWTs in Go?

Go is fast, clean, and great for building APIs, perfect match for JWTs. Instead of maintaining clunky server-side sessions, you issue a token and validate it with every request. Stateless. Scalable. Simple.

But, and this is a big but, it’s only simple if you implement it right.

🔐 How JWT Authentication Works in Go

Here’s a super simplified flow:

- User logs in with credentials.

- Server validates credentials and generates a JWT.

- User stores the token (usually in localStorage or a cookie).

On every API request, the token is sent in the Authorization header.

- Server validates the token and either allows or denies access.

We used the popular github.com/golang-jwt/jwt/v5 package to do the heavy lifting.

Generating a Token

func GenerateJWT(username string) (string, error) {
     claims := jwt.RegisteredClaims{
        Subject:   username,
        ExpiresAt: jwt.NewNumericDate(time.Now().Add(2 * time.Hour)),
        IssuedAt:  jwt.NewNumericDate(time.Now()),
    }

    token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
    return token.SignedString([]byte("your-secret-key"))
}

Validating a Token

func ValidateJWT(tokenStr string) (*jwt.RegisteredClaims, error) {
    token, err := jwt.ParseWithClaims(tokenStr, &jwt.RegisteredClaims{}, func(t *jwt.Token) (interface{}, error) {
        return []byte("your-secret-key"), nil
    })

    if err != nil || !token.Valid {
        return nil, err
    }

    claims, ok := token.Claims.(*jwt.RegisteredClaims)
    if !ok {
        return nil, errors.New("invalid claims")
    }

    return claims, nil
}

Hard Earned Lessons

Some mistakes we’ve either made or seen others make:

❌ Storing sensitive data (like passwords!) in the JWT payload. Never do this.

❌ Forgetting to set expiration times (exp) - leads to tokens that never die.

❌ Using weak secrets. A JWT signed with mysecret123 is an open invitation to attackers.

Instead:

✅ Use short-lived access tokens + refresh tokens.

✅ Secure your secrets with env vars or vaults.

✅ Always validate all claims, even the ones you don’t think matter.

🔄 Bonus: Token Refreshing

If you’ve ever had to juggle access + refresh tokens, you know it’s not trivial. Go doesn’t magically handle this, you have to build a strategy.

Final Thoughts

JWTs are powerful, but they’re not magic. Go gives you the tools to implement them efficiently, but security is always in the details.

Never trust a token blindly.

Always validate everything.

And don’t forget the human side of engineering, code is only part of the equation.