feat: add Multiple Custom Domains (MCD) support and fix JWT verification

Author: kishore7snehil

.gitignore

@@ -24,4 +24,6 @@ test.py
 test-script.py
 .coverage
 coverage.xml
-
+examples/mcd-poc
+IMPLEMENTATION_NOTES.md
+examples/MCD_DEVELOPER_GUIDE.md

examples/MCD.md

@@ -0,0 +1,139 @@
+# Multiple Custom Domains (MCD) Guide
+
+This guide explains how to implement Multiple Custom Domain (MCD) support using the Auth0 Python SDKs.
+
+## What is MCD?
+
+Multiple Custom Domains (MCD) allows your application to serve different organizations or tenants from different hostnames, each mapping to a different Auth0 tenant/domain.
+
+**Example:**
+- `https://acme.yourapp.com` → Auth0 tenant: `acme.auth0.com`
+- `https://globex.yourapp.com` → Auth0 tenant: `globex.auth0.com`
+
+Each tenant gets its own branded login experience while using a single application codebase.
+
+## Configuration Methods
+
+### Method 1: Static Domain (Single Tenant)
+
+For applications with a single Auth0 domain:
+
+```python
+from auth0_server_python import ServerClient
+
+client = ServerClient(
+    domain="your-tenant.auth0.com",  # Static string
+    client_id="your_client_id",
+    client_secret="your_client_secret",
+    secret="your_encryption_secret"
+)
+```
+
+### Method 2: Dynamic Domain Resolver (MCD)
+
+For MCD support, provide a domain resolver function that receives a `DomainResolverContext`:
+
+```python
+from auth0_server_python import ServerClient
+from auth0_server_python.auth_types import DomainResolverContext
+
+# Map your app hostnames to Auth0 domains
+DOMAIN_MAP = {
+    "acme.yourapp.com": "acme.auth0.com",
+    "globex.yourapp.com": "globex.auth0.com",
+}
+DEFAULT_DOMAIN = "default.auth0.com"
+
+async def domain_resolver(context: DomainResolverContext) -> str:
+    """
+    Resolve Auth0 domain based on request hostname.
+    
+    Args:
+        context: Contains request_url and request_headers
+        
+    Returns:
+        Auth0 domain string (e.g., "acme.auth0.com")
+    """
+    # Extract hostname from request headers
+    if not context.request_headers:
+        return DEFAULT_DOMAIN
+    
+    host = context.request_headers.get('host', DEFAULT_DOMAIN)
+    host_without_port = host.split(':')[0]
+    
+    # Look up Auth0 domain
+    return DOMAIN_MAP.get(host_without_port, DEFAULT_DOMAIN)
+
+client = ServerClient(
+    domain=domain_resolver,  # Callable function
+    client_id="your_client_id",
+    client_secret="your_client_secret",
+    secret="your_encryption_secret"
+)
+```
+
+## DomainResolverContext
+
+The `DomainResolverContext` object provides request information to your resolver:
+
+| Property | Type | Description |
+|----------|------|-------------|
+| `request_url` | `Optional[str]` | Full request URL (e.g., "https://acme.yourapp.com/auth/login") |
+| `request_headers` | `Optional[dict[str, str]]` | Request headers dictionary |
+
+**Common headers:**
+- `host`: Request hostname (e.g., "acme.yourapp.com")
+- `x-forwarded-host`: Original host when behind proxy/load balancer
+
+**Example usage:**
+
+```python
+async def domain_resolver(context: DomainResolverContext) -> str:
+    # Check if we have request headers
+    if not context.request_headers:
+        return DEFAULT_DOMAIN
+    
+    # Use x-forwarded-host if behind proxy, otherwise use host
+    host = (context.request_headers.get('x-forwarded-host') or 
+            context.request_headers.get('host', ''))
+    
+    # Remove port number if present
+    hostname = host.split(':')[0].lower()
+    
+    # Look up in mapping
+    return DOMAIN_MAP.get(hostname, DEFAULT_DOMAIN)
+```
+
+## Error Handling
+
+### DomainResolverError
+
+The domain resolver should return a valid Auth0 domain string. Invalid returns will raise `DomainResolverError`:
+
+```python
+from auth0_server_python.error import DomainResolverError
+
+async def domain_resolver(context: DomainResolverContext) -> str:
+    try:
+        domain = lookup_domain_from_db(context)
+        
+        if not domain:
+            # Return default instead of None
+            return DEFAULT_DOMAIN
+        
+        return domain  # Must be a non-empty string
+        
+    except Exception as e:
+        # Log error and return default
+        logger.error(f"Domain resolution failed: {e}")
+        return DEFAULT_DOMAIN
+```
+
+**Invalid return values that raise `DomainResolverError`:**
+- `None`
+- Empty string `""`
+- Non-string types (int, list, dict, etc.)
+
+**Exceptions raised by your resolver:**
+- Automatically wrapped in `DomainResolverError`
+- Original exception accessible via `.original_error`