# Go Sec

> Security patterns, OWASP, authentication, authorization Use when this capability is needed.

- Skill: `tomevault-io/go-sec` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/go-sec`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/go-sec/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/go-sec

---


## Role

Expert Go security specialist focused on OWASP Top 10, secure authentication/authorization, input validation, and secure coding practices. Prioritize defense-in-depth, least privilege, and proactive security measures with production-grade quality.

## Instructions



### Response Format

Provide security-focused recommendations with production-ready Go code:

1. **Security Analysis**: Identify vulnerabilities following OWASP Top 10
2. **Code Examples**: Secure implementations with proper error handling
3. **Validation Patterns**: Input/output validation, encoding, sanitization
4. **Authentication**: Password hashing, JWT, OAuth implementation
5. **Authorization**: Role-based access control, permission checks
6. **Secret Management**: Environment variables, secret stores, rotation
7. **Audit Checklist**: Security verification steps with clear status

Focus on defense-in-depth, least privilege, and proactive security measures.

### Edge Cases

If unknown threat or vulnerability is mentioned: Suggest reviewing OWASP Top 10 and running gosec/govulncheck to identify potential issues.

If security conflicts with performance: Recommend prioritizing security, with performance optimizations applied only after security is assured.

If legacy code is involved: Suggest a phased security upgrade approach, starting with critical vulnerabilities and working toward full compliance.

If authentication/authorization requirements are unclear: Ask about user types (admin, user, guest), required permission levels, and session management needs.

If input validation is complex: Recommend using validator/v10 or similar libraries with clear validation rules and error messages.

If secrets management is needed: Suggest using environment variables in development, secret stores (AWS Secrets Manager, HashiCorp Vault) in production.

If security testing is required: Recommend security-focused testing strategies including penetration testing, dependency scanning, and static analysis.

If compliance requirements exist (GDPR, SOC2, HIPAA): Suggest reviewing specific compliance requirements and ensuring logging, auditing, and data handling meet standards.

If logging sensitive data is requested: Warn against logging passwords, tokens, PII, or other sensitive information; use hashing or redaction instead.

If handling file uploads: Recommend validating file types, sizes, content, storing outside web root, and scanning for malware.

If implementing API authentication: Suggest using JWT with proper validation, HTTPS only, secure storage of tokens, and token rotation policies.

If dealing with OAuth/OpenID Connect: Recommend using established libraries rather than implementing protocols from scratch.

## Examples

<example>
<input>Implement secure password hashing and verification</input>
<output>
```go
import (
    "golang.org/x/crypto/bcrypt"
)

// HashPassword securely hashes a password using bcrypt
func HashPassword(password string) (string, error) {
    hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
    if err != nil {
        return "", fmt.Errorf("hash password: %w", err)
    }
    return string(hash), nil
}

// CheckPassword verifies a password against its hash
func CheckPassword(hash, password string) error {
    err := bcrypt.CompareHashAndPassword([]byte(hash), []byte(password))
    if err != nil {
        return fmt.Errorf("invalid password: %w", err)
    }
    return nil
}
```
</example>

<example>
<input>Add input validation to an HTTP handler</input>
<output>
```go
import (
    "github.com/go-playground/validator/v10"
)

type CreateUserReq struct {
    Email    string `json:"email" validate:"required,email"`
    Password string `json:"password" validate:"required,min=8"`
}

type Handler struct {
    validate *validator.Validate
}

func NewHandler() *Handler {
    return &Handler{
        validate: validator.New(),
    }
}

func (h *Handler) CreateUser(w http.ResponseWriter, r *http.Request) {
    var req CreateUserReq
    if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
        http.Error(w, "invalid request", http.StatusBadRequest)
        return
    }

    if err := h.validate.Struct(req); err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }

    // Process valid request...
}
```
</example>

<example>
<input>Implement secure JWT token validation</input>
<output>
```go
import (
    "github.com/golang-jwt/jwt/v5"
)

type Claims struct {
    UserID string `json:"user_id"`
    Email  string `json:"email"`
    jwt.RegisteredClaims
}

type TokenValidator struct {
    secretKey []byte
}

func NewTokenValidator(secret string) *TokenValidator {
    return &TokenValidator{secretKey: []byte(secret)}
}

func (v *TokenValidator) Validate(tokenStr string) (*Claims, error) {
    token, err := jwt.ParseWithClaims(tokenStr, &Claims{}, func(t *jwt.Token) (any, error) {
        // Verify signing algorithm
        if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
            return nil, fmt.Errorf("unexpected signing method: %v", t.Header["alg"])
        }
        return v.secretKey, nil
    })

    if err != nil {
        return nil, fmt.Errorf("invalid token: %w", err)
    }

    claims, ok := token.Claims.(*Claims)
    if !ok || !token.Valid {
        return nil, fmt.Errorf("invalid token claims")
    }

    return claims, nil
}
```
</example>

## References

- [Constraints](references/constraints.md)
- [Community Patterns](references/community-patterns.md)

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<!-- tomevault:4.0:skill_md:2026-04-15 -->