Application Security

What I do

• Implement secure software development lifecycle (SDLC)
• Identify and mitigate application vulnerabilities
• Design and implement authentication/authorization systems
• Conduct security code reviews
• Implement input validation and output encoding
• Configure web application firewalls
• Handle sensitive data securely
• Implement secure session management

When to use me

When building, reviewing, or securing web applications, APIs, or any software that processes user data or requires protection against attacks.

Secure Development Lifecycle

Threat Modeling

class ThreatModel:
    """Identify threats during design phase"""
    
    def __init__(self, application: str):
        self.application = application
        self.threats = []
    
    def add_data_flow(self, source: str, dest: str, data_type: str):
        """Model data flows to identify trust boundaries"""
        self.threats.append({
            'source': source,
            'destination': dest,
            'data_type': data_type,
            'trust_boundary': self._is_trust_boundary(source, dest)
        })
    
    def _is_trust_boundary(self, source: str, dest: str) -> bool = ['app_server', 'database']
:
        trusted        untrusted = ['user_browser', 'external_api']
        return (source in untrusted and dest in trusted) or \
               (source in trusted and dest in untrusted)

Input Validation

from pydantic import BaseModel, validator
import re

class UserRegistration(BaseModel):
    username: str
    email: str
    password: str
    
    @validator('email')
    def validate_email(cls, v):
        pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
        if not re.match(pattern, v):
            raise ValueError('Invalid email format')
        return v.lower()
    
    @validator('password')
    def validate_password(cls, v):
        if len(v) < 12:
            raise ValueError('Password must be at least 12 characters')
        if not re.search(r'[A-Z]', v):
            raise ValueError('Password must contain uppercase')
        if not re.search(r'[0-9]', v):
            raise ValueError('Password must contain numbers')
        return v

Output Encoding

import html

def safe_render(user_input: str) -> str:
    return html.escape(user_input)

Authentication Patterns

MFA Implementation

import pyotp

class MFAProvider:
    def __init__(self, secret: str = None):
        self.secret = secret or pyotp.random_base32()
    
    def get_qr_uri(self, account_name: str) -> str:
        return pyotp.totp(self.secret).provisioning_uri(
            account_name, issuer_name="MyApp"
        )
    
    def verify(self, token: str) -> bool:
        totp = pyotp.TOTP(self.secret)
        return totp.verify(token, valid_window=1)

Session Management

import secrets
from datetime import datetime, timedelta

class SecureSessionManager:
    def __init__(self):
        self.sessions = {}
        self.session_timeout = timedelta(hours=1)
    
    def create_session(self, user_id: str) -> str:
        session_id = secrets.token_hex(32)
        self.sessions[session_id] = {
            'user_id': user_id,
            'created_at': datetime.now(),
            'last_activity': datetime.now()
        }
        return session_id

Authorization Models

RBAC Implementation

from enum import Enum
from functools import wraps

class Role(Enum):
    ADMIN = "admin"
    USER = "user"
    GUEST = "guest"

class Permission(Enum):
    READ = "read"
    WRITE = "write"
    DELETE = "delete"

ROLE_PERMISSIONS = {
    Role.ADMIN: {Permission.READ, Permission.WRITE, Permission.DELETE},
    Role.USER: {Permission.READ, Permission.WRITE},
    Role.GUEST: {Permission.READ}
}

def require_permission(permission: Permission):
    def decorator(f):
        @wraps(f)
        def decorated_function(*args, **kwargs):
            if not current_user.has_permission(permission):
                abort(403)
            return f(*args, **kwargs)
        return decorated_function
    return decorator