Zero Trust and Continuous Authorization

Zero Trust principles applied to API authorization mean never trusting requests based solely on network location or previous authentication. Every API request requires authorization verification, regardless of source. This approach protects against various threats including compromised credentials, insider threats, and lateral movement after initial compromise.

Continuous authorization extends beyond single request authorization to monitor ongoing sessions. Risk signals like unusual behavior patterns, impossible travel scenarios, or device changes can trigger re-authorization requirements. This dynamic approach adapts security posture to changing risk levels without impacting legitimate users unnecessarily.

# Python example of continuous authorization
import time
from datetime import datetime, timedelta

class ContinuousAuthorizationEngine:
    def __init__(self):
        self.risk_threshold = 0.7
        self.session_data = {}
    
    def evaluate_request(self, session_id, request_context):
        risk_score = self.calculate_risk_score(session_id, request_context)
        
        if risk_score > self.risk_threshold:
            return {
                'authorized': False,
                'reason': 'High risk detected',
                'required_action': 'reauthenticate'
            }
        
        # Update session data
        self.update_session(session_id, request_context)
        
        return {
            'authorized': True,
            'risk_score': risk_score
        }
    
    def calculate_risk_score(self, session_id, context):
        score = 0.0
        session = self.session_data.get(session_id, {})
        
        # Check for location anomalies
        if session.get('last_location'):
            distance = self.calculate_distance(session['last_location'], context['location'])
            time_diff = (context['timestamp'] - session['last_timestamp']).seconds
            
            # Impossible travel check
            if distance / time_diff > 500:  # km/hour
                score += 0.5
        
        # Check for unusual access patterns
        if context['resource'] not in session.get('accessed_resources', []):
            score += 0.2
        
        # Check for time-based anomalies
        current_hour = datetime.now().hour
        if current_hour not in session.get('active_hours', range(9, 18)):
            score += 0.3
        
        return min(score, 1.0)

Authorization is not a one-time decision but an ongoing process throughout an API session. The next chapter explores how HTTPS and transport layer security provide the secure foundation upon which authentication and authorization mechanisms depend.## HTTPS and Transport Layer Security for APIs

Transport Layer Security (TLS) and its predecessor SSL form the foundation of secure API communication. While authentication and authorization control access, TLS ensures that data transmitted between clients and APIs remains confidential and tamper-proof. This chapter provides a comprehensive guide to implementing and optimizing HTTPS for APIs, covering everything from basic setup to advanced security configurations.