diff --git a/api/migrations/0003_todo_collabs.py b/api/migrations/0003_todo_collabs.py
new file mode 100644
index 0000000..fd47a61
--- /dev/null
+++ b/api/migrations/0003_todo_collabs.py
@@ -0,0 +1,20 @@
+# Generated by Django 3.0.7 on 2021-08-03 07:03
+
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+        ('api', '0002_todo_creator'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='todo',
+            name='collabs',
+            field=models.ManyToManyField(related_name='collaborators', to=settings.AUTH_USER_MODEL),
+        ),
+    ]
diff --git a/api/models.py b/api/models.py
index ab3ca0a..eafc8fe 100644
--- a/api/models.py
+++ b/api/models.py
@@ -5,6 +5,6 @@
 class Todo(models.Model):
     creator = models.ForeignKey(User, on_delete=models.CASCADE)
     title = models.CharField(max_length=255)
-
+    collabs = models.ManyToManyField(User,related_name='collaborators')
     def __str__(self):
         return self.title
\ No newline at end of file
diff --git a/api/serializers.py b/api/serializers.py
index ffd9d3a..7dc7287 100644
--- a/api/serializers.py
+++ b/api/serializers.py
@@ -1,3 +1,4 @@
+from django.contrib.auth.models import User
 from rest_framework import serializers
 from .models import Todo
 
@@ -23,7 +24,65 @@ def save(self, **kwargs):
         user = self.context['request'].user
         title = data['title']
         todo = Todo.objects.create(creator=user, title=title)
-    
+        data['id'] = todo.id
+
     class Meta:
         model = Todo
         fields = ('id', 'title',)
+
+class TodoSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = Todo
+        fields = ('id','title',)
+
+class TodoAddCollabSerializer(serializers.Serializer):
+    username = serializers.CharField()
+    def validate(self, attrs):
+        username = attrs.get('username')
+        todo = self.context.get('todo')
+
+        if username == todo.creator.username:
+            raise serializers.ValidationError({
+                'Creator': 'Cannot add creator of todo as a collaborator'
+            })
+
+        if username not in [i.username for i in User.objects.all()]:
+            raise serializers.ValidationError({
+                'username': 'Such a user does not exist'
+            })
+        
+        if username in [i.username for i in todo.collabs.all()]:
+            raise serializers.ValidationError({
+                'username': 'User is already a collaborator to this todo'
+            })
+        return attrs
+
+    def save(self,todo):
+        newCollab = User.objects.get(username=self.validated_data.get('username'))
+        self.context.get('todo').collabs.add(newCollab)
+
+class TodoRemoveCollabSerializer(serializers.Serializer):
+    username = serializers.CharField()
+    def validate(self, attrs):
+        username = attrs.get('username')
+        todo = self.context.get('todo')
+
+        if username == todo.creator.username:
+            raise serializers.ValidationError({
+                'Creator': 'Given user is creator of this todo'
+            })
+
+        if username not in [i.username for i in User.objects.all()]:
+            raise serializers.ValidationError({
+                'username': 'Such a user does not exist'
+            })
+        
+        if username not in [i.username for i in todo.collabs.all()]:
+            raise serializers.ValidationError({
+                'username': 'User is not a collaborator to this todo'
+            })
+        return attrs
+
+    def save(self,todo):
+        newCollab = User.objects.get(username=self.validated_data.get('username'))
+        self.context.get('todo').collabs.remove(newCollab)
diff --git a/api/urls.py b/api/urls.py
index 72f4978..ad3b6b7 100644
--- a/api/urls.py
+++ b/api/urls.py
@@ -1,5 +1,5 @@
 from django.urls import path
-from .views import TodoCreateView
+from .views import (TodoCreateView,TodoListView,TodoDetail,TodoAddCollabs,TodoRemoveCollabs)
 
 """
 TODO:
@@ -9,4 +9,8 @@
 
 urlpatterns = [
     path('todo/create/', TodoCreateView.as_view()),
+    path('todo/',TodoListView.as_view()),
+    path('todo/<int:id>/', TodoDetail.as_view()),
+    path('todo/<int:id>/add-collaborators/',TodoAddCollabs.as_view()),
+    path('todo/<int:id>/remove-collaborators/',TodoRemoveCollabs.as_view()),
 ]
\ No newline at end of file
diff --git a/api/views.py b/api/views.py
index d676c64..faf9fb4 100644
--- a/api/views.py
+++ b/api/views.py
@@ -1,8 +1,9 @@
-from rest_framework import generics
-from rest_framework import permissions
-from rest_framework import status
+from django.db.models import Q
+from rest_framework import (generics, permissions, status)
+from django.http import Http404
 from rest_framework.response import Response
-from .serializers import TodoCreateSerializer
+from rest_framework.views import APIView
+from .serializers import (TodoCreateSerializer, TodoSerializer,TodoAddCollabSerializer,TodoRemoveCollabSerializer)
 from .models import Todo
 
 
@@ -32,4 +33,112 @@ def post(self, request):
         serializer = self.get_serializer(data=request.data)
         serializer.is_valid(raise_exception=True)
         serializer.save()
-        return Response(status=status.HTTP_200_OK)
+        return Response(serializer.data,status=status.HTTP_200_OK)
+
+class TodoListView(generics.GenericAPIView):
+    permission_classes = (permissions.IsAuthenticated, )
+    serializer_class = TodoSerializer
+    
+    # PRINTING ALL TODO IN WHICH AUTHENTICATED USER IS CREATOR OR CONTRIBUTOR
+    def get(self,request):
+        todos = Todo.objects.filter(Q(creator=request.user) | Q(collabs=request.user))
+        serializer = self.get_serializer(todos,many=True)
+        return Response(serializer.data)
+
+class TodoDetail(APIView):
+    permission_classes = (permissions.IsAuthenticated, )
+    def get_todo(self, id):
+        try:
+            return Todo.objects.get(id=id)
+        except Todo.DoesNotExist:
+            raise Http404
+    
+    def check_user(self,todo):
+        if todo.creator == self.request.user:
+            return 1
+        if self.request.user in todo.collabs.all():
+            return 1
+        return 0
+
+    def get(self, request, id):
+        todo = self.get_todo(id)
+        if self.check_user(todo)==0:
+            return Response(status=401)
+        serializer = TodoSerializer(todo)
+        return Response(serializer.data)
+    
+    def put(self, request, id):
+        todo = self.get_todo(id)
+        if self.check_user(todo)==0:
+            return Response(status=401)
+        serializer = TodoSerializer(todo, data=request.data)
+        if serializer.is_valid():
+            serializer.save()
+            return Response(serializer.data)
+        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
+    
+    def patch(self, request, id):
+        todo = self.get_todo(id)
+        if self.check_user(todo)==0:
+            return Response(status=401)
+        serializer = TodoSerializer(todo, data=request.data)
+        if serializer.is_valid():
+            serializer.save()
+            return Response(serializer.data)
+        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
+    
+    def delete(self, request, id):
+        todo = self.get_todo(id)
+        if self.check_user(todo)==0:
+            return Response(status=401)
+        todo.delete()
+        return Response(status=status.HTTP_204_NO_CONTENT)
+
+
+class TodoAddCollabs(APIView):
+    permission_classes = (permissions.IsAuthenticated, )
+    def get_todo(self, id):
+        try:
+            return Todo.objects.get(id=id)
+        except Todo.DoesNotExist:
+            raise Http404
+
+    def check_user(self,todo):
+        if todo.creator == self.request.user:
+            return 1
+        return 0
+
+    def post(self,request,id):
+        todo = self.get_todo(id)
+        if self.check_user(todo)==0:
+            return Response(status=401)
+
+        serializer = TodoAddCollabSerializer(data = request.data, context={'todo':todo})      
+        if serializer.is_valid():
+            serializer.save(todo)
+            return Response({'info': 'New Collaborator Added'})
+        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
+
+class TodoRemoveCollabs(APIView):
+    permission_classes = (permissions.IsAuthenticated, )
+    def get_todo(self, id):
+        try:
+            return Todo.objects.get(id=id)
+        except Todo.DoesNotExist:
+            raise Http404
+
+    def check_user(self,todo):
+        if todo.creator == self.request.user:
+            return 1
+        return 0
+
+    def post(self,request,id):
+        todo = self.get_todo(id)
+        if self.check_user(todo)==0:
+            return Response(status=401)
+
+        serializer = TodoRemoveCollabSerializer(data = request.data, context={'todo':todo})      
+        if serializer.is_valid():
+            serializer.save(todo)
+            return Response({'info': 'Collaborator Removed'})
+        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
diff --git a/authentication/serializers.py b/authentication/serializers.py
index 47264af..2232798 100644
--- a/authentication/serializers.py
+++ b/authentication/serializers.py
@@ -1,5 +1,7 @@
+from django.db.models import fields
 from rest_framework import serializers
 from django.contrib.auth import authenticate
+from django.utils.translation import gettext_lazy as _
 from django.contrib.auth.models import User
 
 
@@ -9,15 +11,50 @@ class TokenSerializer(serializers.Serializer):
 
 class LoginSerializer(serializers.Serializer):
     # TODO: Implement login functionality
-    pass
-
+    username = serializers.CharField()
+    password = serializers.CharField(style={'input_type': 'password'},trim_whitespace=False)
+
+    def validate(self, attrs):
+        username = attrs.get('username')
+        password = attrs.get('password')
+
+        if username and password:
+            user = authenticate(request=self.context.get('request'),username=username, password=password)
+            if not user:
+                msg = _('Unable to log in with provided credentials.')
+                raise serializers.ValidationError(msg, code='authorization')
+        else:
+            msg = _('Must include "username" and "password".')
+            raise serializers.ValidationError(msg, code='authorization')
+
+        attrs['user'] = user
+        return attrs
+    
 
 class RegisterSerializer(serializers.Serializer):
     # TODO: Implement register functionality
-    pass
+    first_name = serializers.CharField(max_length=100,required=True)
+    email = serializers.EmailField(required=True)
+    username = serializers.CharField(max_length=150,required=True)
+    password = serializers.CharField(
+        write_only=True,
+        required=True,
+        style={'input_type': 'password', 'placeholder': 'Password'}
+    )
+    
+    def create(self, validated_data):
+        return User.objects.create(**validated_data)
+    
 
 
 class UserSerializer(serializers.ModelSerializer):
     # TODO: Implement the functionality to display user details
-    pass
+    class Meta:
+        model = User
+        fields = ['id', 'username', 'first_name', 'email']
+
+    
+
+
+        
     
\ No newline at end of file
diff --git a/authentication/views.py b/authentication/views.py
index d748434..17e6e32 100644
--- a/authentication/views.py
+++ b/authentication/views.py
@@ -1,12 +1,12 @@
-from rest_framework import permissions
-from rest_framework import generics
-from rest_framework import status
+from django.contrib.auth.models import User
+from rest_framework import permissions, serializers, generics, status
+from rest_framework.decorators import permission_classes
+from rest_framework.permissions import IsAuthenticated
 from rest_framework.response import Response
 from rest_framework.authtoken.models import Token
 from .serializers import (
     LoginSerializer, RegisterSerializer, UserSerializer, TokenSerializer)
 
-
 def create_auth_token(user):
     """
     Returns the token required for authentication for a user.
@@ -21,7 +21,11 @@ class LoginView(generics.GenericAPIView):
     Implement login functionality, taking username and password
     as input, and returning the Token.
     """
-    pass
+    def post(self,request):
+        serializer = LoginSerializer(data = request.data)
+        serializer.is_valid(raise_exception=True)
+        user = serializer.validated_data['user']
+        return Response({ "token": str(create_auth_token(user)) }, status=200)
 
 
 class RegisterView(generics.GenericAPIView):
@@ -30,13 +34,34 @@ class RegisterView(generics.GenericAPIView):
     Implement register functionality, registering the user by
     taking his details, and returning the Token.
     """
-    pass
-
+    def post(self,request):
+        serializer = RegisterSerializer(data={
+            'first_name':request.data['name'],
+            'email':request.data['email'],
+            'username':request.data['username'],
+            'password':request.data['password'],
+        })
+        if serializer.is_valid():
+            try: 
+                newUser = serializer.save()
+            except :
+                return Response({'username': 'This username is already taken.'}, status=400)
+            return Response({ "token": str(create_auth_token(newUser)) }, status=201)
+        return Response(serializer.errors,status=400)
 
-class UserProfileView(generics.RetrieveAPIView):
+class UserProfileView(generics.GenericAPIView):
     """
     TODO:
     Implement the functionality to retrieve the details
     of the logged in user.
     """
-    pass
\ No newline at end of file
+    permission_classes = (permissions.IsAuthenticated, )
+    def post(self,request):
+        user = User.objects.get(id=request.user.id)
+        serializer = UserSerializer(user)
+        return Response({
+            "id":  serializer.data['id'],
+	        "name":  serializer.data['first_name'],
+	        "email":  serializer.data['email'],
+	        "username":  serializer.data['username']
+        })
\ No newline at end of file
diff --git a/todo/settings.py b/todo/settings.py
index 8359271..6ca1fa1 100644
--- a/todo/settings.py
+++ b/todo/settings.py
@@ -63,9 +63,9 @@
 CORS_ORIGIN_ALLOW_ALL = True
 
 REST_FRAMEWORK = {
-    'DEFAULT_AUTHENTICATION_CLASSES': (
+    'DEFAULT_AUTHENTICATION_CLASSES': [
         'rest_framework.authentication.TokenAuthentication',
-    )
+    ],
 }
 
 ROOT_URLCONF = 'todo.urls'