✨ [#80] Support configuring basic auth for token endpoint

Certain OIDC providers require the client credentials to be sent
in the Basic Auth request header rather than in the request
body. This is now configurable in the admin.

mozilla_django_oidc_db/admin.py

@@ -35,6 +35,7 @@ class OpenIDConnectConfigAdmin(SingletonModelAdmin):
                     "oidc_op_jwks_endpoint",
                     "oidc_op_authorization_endpoint",
                     "oidc_op_token_endpoint",
+                    "oidc_token_use_basic_auth",
                     "oidc_op_user_endpoint",
                 )
             },

mozilla_django_oidc_db/migrations/0015_openidconnectconfig_oidc_token_use_basic_auth.py

@@ -0,0 +1,22 @@
+# Generated by Django 3.2.23 on 2024-02-05 16:51
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("mozilla_django_oidc_db", "0014_alter_openidconnectconfig_groups_claim"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="openidconnectconfig",
+            name="oidc_token_use_basic_auth",
+            field=models.BooleanField(
+                default=False,
+                help_text="If enabled, the client ID and secret are sent in the HTTP Basic auth header when obtaining the access token. Otherwise, they are sent in the request body.",
+                verbose_name="Use Basic auth for token endpoint",
+            ),
+        ),
+    ]

mozilla_django_oidc_db/models.py

@@ -161,6 +161,15 @@ class OpenIDConnectConfigBase(SingletonModel):
         max_length=1000,
         help_text=_("URL of your OpenID Connect provider token endpoint"),
     )
+    oidc_token_use_basic_auth = models.BooleanField(
+        _("Use Basic auth for token endpoint"),
+        default=False,
+        help_text=_(
+            "If enabled, the client ID and secret are sent in the HTTP Basic auth "
+            "header when obtaining the access token. Otherwise, they are sent in the "
+            "request body.",
+        ),
+    )
     oidc_op_user_endpoint = models.URLField(
         _("User endpoint"),
         max_length=1000,