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cors ​

Got it! I’ll go through each CORS configuration setting in Nexios, explaining what it does and how it impacts requests.

Basic CORS Configuration in Nexios ​

Before diving into individual settings, here’s a simple CORS setup using MakeConfig:

python
from nexios import MakeConfig
from nexios.middlewares.cors import CORSMiddleware
config = MakeConfig({
    "cors": {
        "allow_origins": ["https://example.com"],
    "allow_methods": ["GET", "POST"],
    "allow_headers": ["Authorization", "X-Requested-With"],
    "allow_credentials": True,
    "max_age": 600,
    "debug": True
    }
})
app = NexiosApp(config = config)

we can break it down further:

allow_origins ​

  • Purpose: Specifies which domains can access the API.

  • Example:

    python
    config.cors["allow_origins"] = ["https://example.com", "https://another-site.com"]

  • Special cases:

    • Use ["*"] to allow requests from any origin (not safe if credentials are enabled).
    • If an origin is not listed here, the request will be blocked.

blacklist_origins ​

  • Purpose: Specifies which origins should be blocked, even if they match allow_origins.

  • Example:

    python
    config.cors["blacklist_origins"] = ["https://bad-actor.com"]

  • Use case: If you allow all origins (["*"]), but want to exclude specific ones.

allow_methods ​

  • Purpose: Defines which HTTP methods (GET, POST, etc.) are allowed in cross-origin requests.

  • Example:

    python
    config.cors["allow_methods"] = ["GET", "POST", "PUT"]

  • Default: All methods (["DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT"]) are allowed.

allow_headers ​

  • Purpose: Specifies which request headers are permitted in cross-origin requests.

  • Example:

    python
    config.cors["allow_headers"] = ["Authorization", "X-Custom-Header"]

  • Default: Basic headers like Accept, Content-Type, etc., are always allowed.

blacklist_headers ​

  • Purpose: Defines headers that should not be allowed in requests.

  • Example:

    python
    config.cors["blacklist_headers"] = ["X-Disallowed-Header"]

  • Use case: If you allow most headers but want to restrict specific ones.

allow_credentials ​

  • Purpose: Determines whether credentials (cookies, authorization headers) are allowed in requests.

  • Example:

    python
    config.cors["allow_credentials"] = True

  • Important:

    • If True, the browser allows requests with credentials (e.g., session cookies).
    • If True, allow_origins cannot be "*" (security restriction).
    • If False, credentials are blocked.

allow_origin_regex ​

  • Purpose: Uses a regex pattern to match allowed origins dynamically.

  • Example:

    python
    config.cors["allow_origin_regex"] = r"https://.*\.trusted-site\.com"

  • Use case: When you want to allow multiple subdomains without listing them individually.

expose_headers ​

  • Purpose: Specifies which response headers the client is allowed to access.

  • Example:

    python
    config.cors["expose_headers"] = ["X-Response-Time"]

  • Default: Only basic headers are exposed unless configured.

max_age ​

  • Purpose: Defines how long the preflight (OPTIONS) response can be cached.

  • Example:

    python
    config.cors["max_age"] = 600  # Cache for 10 minutes

  • Impact: Reduces unnecessary preflight requests for frequent API calls.

strict_origin_checking ​

  • Purpose: If enabled, requests must include an Origin header.

  • Example:

    python
    config.cors["strict_origin_checking"] = True

  • Use case: When you want to strictly enforce CORS checks, especially for security.

debug ​

  • Purpose: Enables logging to troubleshoot CORS issues.

  • Example:

    python
    config.cors["debug"] = True

  • Impact:

    • Prints logs when a request is blocked due to CORS.
    • Useful for debugging in development.

custom_error_status & custom_error_messages ​

  • Purpose: Allows custom error handling for CORS failures.

  • Example:

    python
    config.cors["custom_error_status"] = 403
config.cors["custom_error_messages"] = {
    "disallowed_origin": "This origin is not allowed.",
    "missing_origin": "The request is missing an origin."
}

  • Use case: When you want meaningful error messages instead of generic CORS errors.