Modify ObtainAuthToken to use the User model's USERNAME_FIELD and password for authentication instead of assuming username and password.

docs/api-guide/authentication.md

@@ -212,7 +212,7 @@ The `obtain_auth_token` view will return a JSON response when valid `username` a
 
     { 'token' : '9944b09199c62bcf9418ad846dd0e4bbdfc6ee4b' }
 
-Note that the default `obtain_auth_token` view explicitly uses JSON requests and responses, rather than using default renderer and parser classes in your settings.
+Note that the default `obtain_auth_token` view explicitly uses JSON requests and responses, rather than using default renderer and parser classes in your settings. If you use a `custom User` model as `AUTH_USER_MODEL` in `settings.py`, authentication will use the `USERNAME_FIELD` and `password` defined in your custom model.
 
 By default, there are no permissions or throttling applied to the `obtain_auth_token` view. If you do wish to apply throttling you'll need to override the view class,
 and include them using the `throttle_classes` attribute.

rest_framework/authtoken/serializers.py

@@ -1,32 +1,50 @@
-from django.contrib.auth import authenticate
+from django.contrib.auth import authenticate, get_user_model
 from django.utils.translation import gettext_lazy as _
 
 from rest_framework import serializers
 
+USER_MODEL = get_user_model()
+
 
 class AuthTokenSerializer(serializers.Serializer):
-    username = serializers.CharField(
-        label=_("Username"),
-        write_only=True
-    )
-    password = serializers.CharField(
-        label=_("Password"),
-        style={'input_type': 'password'},
-        trim_whitespace=False,
-        write_only=True
-    )
+    def __init__(self, instance=None, data=None, **kwargs):
+        super().__init__(instance, data=data, **kwargs)
+        self.identifier_fiend_name = USER_MODEL.USERNAME_FIELD
+        if USER_MODEL.get_email_field_name() == self.identifier_fiend_name:
+            self.fields[self.identifier_fiend_name] = serializers.EmailField(
+                label=_(self.identifier_fiend_name.title()),
+                write_only=True
+            )
+        else:
+            self.fields[self.identifier_fiend_name] = serializers.CharField(
+                label=_(self.identifier_fiend_name.title()),
+                write_only=True
+            )
+        self.fields["password"] = serializers.CharField(
+            label=_("Password"),
+            style={'input_type': 'password'},
+            trim_whitespace=False,
+            write_only=True
+        )
+
     token = serializers.CharField(
         label=_("Token"),
         read_only=True
     )
 
     def validate(self, attrs):
-        username = attrs.get('username')
+        identifier_value = attrs.get(self.identifier_fiend_name)
         password = attrs.get('password')
 
-        if username and password:
-            user = authenticate(request=self.context.get('request'),
-                                username=username, password=password)
+        if identifier_value and password:
+            credentials = {
+                self.identifier_fiend_name: identifier_value,
+                "password": password,
+            }
+            user = authenticate(
+                request=self.context.get('request'),
+                **credentials,
+            )
 
             # The authenticate call simply returns None for is_active=False
             # users. (Assuming the default ModelBackend authentication
@@ -35,7 +53,7 @@ def validate(self, attrs):
                 msg = _('Unable to log in with provided credentials.')
                 raise serializers.ValidationError(msg, code='authorization')
         else:
-            msg = _('Must include "username" and "password".')
+            msg = _(f'Must include "{self.identifier_fiend_name}" and "password".')
             raise serializers.ValidationError(msg, code='authorization')
 
         attrs['user'] = user

rest_framework/authtoken/views.py

@@ -1,3 +1,5 @@
+from django.contrib.auth import get_user_model
+
 from rest_framework import parsers, renderers
 from rest_framework.authtoken.models import Token
 from rest_framework.authtoken.serializers import AuthTokenSerializer
@@ -16,15 +18,17 @@ class ObtainAuthToken(APIView):
     serializer_class = AuthTokenSerializer
 
     if coreapi_schema.is_enabled():
+        USER_MODEL = get_user_model()
+        identifier_field_name = USER_MODEL.USERNAME_FIELD
         schema = ManualSchema(
             fields=[
                 coreapi.Field(
-                    name="username",
+                    name=identifier_field_name,
                     required=True,
                     location='form',
                     schema=coreschema.String(
-                        title="Username",
-                        description="Valid username for authentication",
+                        title=identifier_field_name.title(),
+                        description=f"Valid {identifier_field_name} for authentication",
                     ),
                 ),
                 coreapi.Field(