Docs: document DEBUG_API_REQUESTS setting

(And add a system check to warn about its use in production deployment.)

anymail/apps.py

@@ -1,7 +1,7 @@
 from django.apps import AppConfig
 from django.core import checks
 
-from .checks import check_deprecated_settings
+from .checks import check_deprecated_settings, check_insecure_settings
 
 
 class AnymailBaseConfig(AppConfig):
@@ -10,3 +10,4 @@ class AnymailBaseConfig(AppConfig):
 
     def ready(self):
         checks.register(check_deprecated_settings)
+        checks.register(check_insecure_settings)

anymail/checks.py

@@ -1,6 +1,8 @@
 from django.conf import settings
 from django.core import checks
 
+from anymail.utils import get_anymail_setting
+
 
 def check_deprecated_settings(app_configs, **kwargs):
     errors = []
@@ -24,3 +26,18 @@ def check_deprecated_settings(app_configs, **kwargs):
         ))
 
     return errors
+
+
+def check_insecure_settings(app_configs, **kwargs):
+    errors = []
+
+    # anymail.W002: DEBUG_API_REQUESTS can leak private information
+    if get_anymail_setting("debug_api_requests", default=False) and not settings.DEBUG:
+        errors.append(checks.Warning(
+            "You have enabled the ANYMAIL setting DEBUG_API_REQUESTS, which can "
+            "leak API keys and other sensitive data into logs or the console.",
+            hint="You should not use DEBUG_API_REQUESTS in production deployment.",
+            id="anymail.W002",
+        ))
+
+    return errors

docs/help.rst

@@ -44,6 +44,14 @@ often help you pinpoint the problem...
   other than Anymail. And you can look through the :setting:`EMAIL_FILE_PATH`
   file contents afterward to see if you're generating the email you want.
 
+**Examine the raw API communication**
+
+  Sometimes you just want to see exactly what Anymail is telling your ESP to do
+  and how your ESP is responding. In a dev environment, enable the Anymail setting
+  :setting:`DEBUG_API_REQUESTS <ANYMAIL_DEBUG_API_REQUESTS>`
+  to show the raw HTTP requests and responses from (most) ESP APIs. (This is not
+  recommended in production, as it can leak sensitive data into your logs.)
+
 
 .. _contact:
 .. _support:

docs/installation.rst

@@ -299,3 +299,25 @@ For Requests-based Anymail backends, the timeout value used for all API calls to
 The default is 30 seconds. You can set to a single float, a 2-tuple of floats for
 separate connection and read timeouts, or `None` to disable timeouts (not recommended).
 See :ref:`requests:timeouts` in the Requests docs for more information.
+
+
+.. setting:: ANYMAIL_DEBUG_API_REQUESTS
+
+.. rubric:: DEBUG_API_REQUESTS
+
+.. versionadded:: 4.3
+
+When set to `True`, outputs the raw API communication with the ESP, to assist in
+debugging. Each HTTP request and ESP response is dumped to :data:`sys.stdout` once
+the response is received.
+
+.. caution::
+
+    Do not enable :setting:`!DEBUG_API_REQUESTS` in production deployments. The debug
+    output will include your API keys, email addresses, and other sensitive data
+    that you generally don't want to capture in server logs or reveal on the console.
+
+:setting:`!DEBUG_API_REQUESTS` only applies to sending email through Requests-based
+Anymail backends. For other backends, there may be similar debugging facilities
+available in the ESP's API wrapper package (e.g., ``boto3.set_stream_logger`` for
+Amazon SES).

tests/test_checks.py

@@ -2,7 +2,7 @@ from django.core import checks
 from django.test import SimpleTestCase
 from django.test.utils import override_settings
 
-from anymail.checks import check_deprecated_settings
+from anymail.checks import check_deprecated_settings, check_insecure_settings
 
 from .utils import AnymailTestMixin
 
@@ -25,3 +25,16 @@ class DeprecatedSettingsTests(SimpleTestCase, AnymailTestMixin):
             hint="You must update your settings.py.",
             id="anymail.E001",
         )])
+
+
+class InsecureSettingsTests(SimpleTestCase, AnymailTestMixin):
+    @override_settings(ANYMAIL={"DEBUG_API_REQUESTS": True})
+    def test_debug_api_requests_deployed(self):
+        errors = check_insecure_settings(None)
+        self.assertEqual(len(errors), 1)
+        self.assertEqual(errors[0].id, "anymail.W002")
+
+    @override_settings(ANYMAIL={"DEBUG_API_REQUESTS": True}, DEBUG=True)
+    def test_debug_api_requests_debug(self):
+        errors = check_insecure_settings(None)
+        self.assertEqual(len(errors), 0)  # no warning in DEBUG (non-production) config