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Implementing account deduplication

The approach to implementing account deduplication is to override the backend functions / APIs which create a user such that:

• We check if a user already exists with that email.
• If a user does not exist, we call the original implementation; Else
• We return a message to the frontend telling the user why sign up was rejected.

Add the following override logic to ThirdParty and Passwordless config on the backend

NodeJS

Important

For other backend frameworks, you can follow our guide on how to spin up a separate server configured with the SuperTokens backend SDK to authenticate requests and issue session tokens.

GoLang

import ThirdParty from "supertokens-node/recipe/thirdparty"
import Passwordless from "supertokens-node/recipe/passwordless";
import supertokens from "supertokens-node";

let recipeList = [
    Passwordless.init({
        override: {
            apis: (originalImplementation) => {
                return {
                    ...originalImplementation,
                    createCodePOST: async function (input) {
                        if ("email" in input) {
                            let existingUsers = await supertokens.listUsersByAccountInfo(input.tenantId, {
                                email: input.email
                            });
                            if (existingUsers.length === 0) {
                                // this means this email is new so we allow sign up
                                return originalImplementation.createCodePOST!(input);
                            }
                            if (existingUsers.find(u =>
                                u.loginMethods.find(lM => lM.hasSameEmailAs(input.email) && lM.recipeId === "passwordless") !== undefined)) {
                                // this means that the existing user is a passwordless login user. So we allow it
                                return originalImplementation.createCodePOST!(input);
                            }
                            return {
                                status: "GENERAL_ERROR",
                                message: "Seems like you already have an account with another method. Please use that instead."
                            }
                        }
                        // phone number based login, so we allow it.
                        return originalImplementation.createCodePOST!(input);
                    },
                }
            }
        }
    }),
    ThirdParty.init({
        override: {
            functions: (originalImplementation) => {
                return {
                    ...originalImplementation,
                    signInUp: async function (input) {
                        let existingUsers = await supertokens.listUsersByAccountInfo(input.tenantId, {
                            email: input.email
                        });
                        if (existingUsers.length === 0) {
                            // this means this email is new so we allow sign up
                            return originalImplementation.signInUp(input);
                        }
                        if (existingUsers.find(u =>
                            u.loginMethods.find(lM => lM.hasSameThirdPartyInfoAs({
                                id: input.thirdPartyId,
                                userId: input.thirdPartyUserId
                            }) && lM.recipeId === "thirdparty") !== undefined)) {
                            // this means we are trying to sign in with the same social login. So we allow it
                            return originalImplementation.signInUp(input);
                        }
                        // this means that the email already exists with another social or passwordless login method, so we throw an error.
                        throw new Error("Cannot sign up as email already exists");
                    }
                }
            },
            apis: (originalImplementation) => {
                return {
                    ...originalImplementation,
                    signInUpPOST: async function (input) {
                        try {
                            return await originalImplementation.signInUpPOST!(input);
                        } catch (err: any) {
                            if (err.message === "Cannot sign up as email already exists") {
                                // this error was thrown from our function override above.
                                // so we send a useful message to the user
                                return {
                                    status: "GENERAL_ERROR",
                                    message: "Seems like you already have an account with another method. Please use that instead."
                                }
                            }
                            throw err;
                        }
                    }
                }
            }
        }
    })
]

Python

import (
    "errors"

    "github.com/supertokens/supertokens-golang/recipe/passwordless"
    "github.com/supertokens/supertokens-golang/recipe/passwordless/plessmodels"
    "github.com/supertokens/supertokens-golang/recipe/thirdparty"
    "github.com/supertokens/supertokens-golang/recipe/thirdparty/tpmodels"
    "github.com/supertokens/supertokens-golang/supertokens"
)

func main() {
    _ = []supertokens.Recipe{
        passwordless.Init(plessmodels.TypeInput{
            Override: &plessmodels.OverrideStruct{
                APIs: func(originalImplementation plessmodels.APIInterface) plessmodels.APIInterface {
                    originalCreateCodePOST := *originalImplementation.CreateCodePOST

                    (*originalImplementation.CreateCodePOST) = func(email, phoneNumber *string, tenantId string, options plessmodels.APIOptions, userContext supertokens.UserContext) (plessmodels.CreateCodePOSTResponse, error) {
                        if email != nil {
                            thirdPartyExistingUsers, err := thirdparty.GetUsersByEmail(tenantId, *email)
                            if err != nil {
                                return plessmodels.CreateCodePOSTResponse{}, err
                            }

                            if len(thirdPartyExistingUsers) == 0 {
                                // this means this email is either a new user or an existing passwordless user, so we allow
                                return originalCreateCodePOST(email, phoneNumber, tenantId, options, userContext)
                            }

                            return plessmodels.CreateCodePOSTResponse{
                                GeneralError: &supertokens.GeneralErrorResponse{
                                    Message: "Seems like you already have an account with another method. Please use that instead.",
                                },
                            }, nil
                        }
                        // phone number based login, so we allow it.
                        return originalCreateCodePOST(email, phoneNumber, tenantId, options, userContext)
                    }

                    return originalImplementation
                },
            },
        }),
        thirdparty.Init(&tpmodels.TypeInput{
            Override: &tpmodels.OverrideStruct{
                Functions: func(originalImplementation tpmodels.RecipeInterface) tpmodels.RecipeInterface {
                    ogSignInUp := *originalImplementation.SignInUp

                    (*originalImplementation.SignInUp) = func(thirdPartyID string, thirdPartyUserID string, email string, oAuthTokens map[string]interface{}, rawUserInfoFromProvider tpmodels.TypeRawUserInfoFromProvider, tenantId string, userContext *map[string]interface{}) (tpmodels.SignInUpResponse, error) {
                        existingUsers, err := thirdparty.GetUsersByEmail(tenantId, email)
                        if err != nil {
                            return tpmodels.SignInUpResponse{}, err
                        }

                        emailPasswordExistingUser, err := passwordless.GetUserByEmail(tenantId, email)
                        if err != nil {
                            return tpmodels.SignInUpResponse{}, err
                        }

                        if emailPasswordExistingUser != nil {
                            return tpmodels.SignInUpResponse{}, errors.New("Cannot sign up as email already exists")
                        }

                        if len(existingUsers) == 0 {
                            // this means this email is new so we allow sign up
                            return ogSignInUp(thirdPartyID, thirdPartyUserID, email, oAuthTokens, rawUserInfoFromProvider, tenantId, userContext)
                        }

                        isSignIn := false
                        for _, user := range existingUsers {
                            if user.ThirdParty.ID == thirdPartyID && user.ThirdParty.UserID == thirdPartyUserID {
                                // this means we are trying to sign in with the same social login. So we allow it
                                isSignIn = true
                            }
                        }
                        if isSignIn {
                            return ogSignInUp(thirdPartyID, thirdPartyUserID, email, oAuthTokens, rawUserInfoFromProvider, tenantId, userContext)
                        }
                        return tpmodels.SignInUpResponse{}, errors.New("Cannot sign up as email already exists")
                    }

                    return originalImplementation
                },

                APIs: func(originalImplementation tpmodels.APIInterface) tpmodels.APIInterface {
                    originalSignInUpPOST := *originalImplementation.SignInUpPOST

                    (*originalImplementation.SignInUpPOST) = func(provider *tpmodels.TypeProvider, input tpmodels.TypeSignInUpInput, tenantId string, options tpmodels.APIOptions, userContext *map[string]interface{}) (tpmodels.SignInUpPOSTResponse, error) {

                        resp, err := originalSignInUpPOST(provider, input, tenantId, options, userContext)

                        if err != nil && err.Error() == "Cannot sign up as email already exists" {
                            // this error was thrown from our function override above.
                            // so we send a useful message to the user
                            return tpmodels.SignInUpPOSTResponse{
                                GeneralError: &supertokens.GeneralErrorResponse{
                                    Message: "Seems like you already have an account with another method. Please use that instead.",
                                },
                            }, nil
                        }

                        return resp, err
                    }

                    return originalImplementation
                },
            },
        }),
    }
}

Other Frameworks

from supertokens_python import init, InputAppInfo
from supertokens_python.types import GeneralErrorResponse
from supertokens_python.recipe import passwordless, thirdparty
from supertokens_python.recipe.passwordless.asyncio import get_user_by_email as get_users_by_email_passwordless
from supertokens_python.recipe.thirdparty.asyncio import get_users_by_email as get_users_by_email_thirdparty
from supertokens_python.recipe.passwordless.interfaces import APIInterface as PasswordlessAPIInterface, APIOptions as PasswordlessAPIOptions
from supertokens_python.recipe.thirdparty.interfaces import RecipeInterface, SignInUpOkResult, APIInterface as ThirdPartyAPIInterface, APIOptions as ThirdPartyAPIOptions
from typing import Union, Dict, Any
from supertokens_python.recipe.thirdparty.provider import Provider, RedirectUriInfo
from supertokens_python.recipe.thirdparty.types import RawUserInfoFromProvider

def override_thirdparty_functions(original_implementation: RecipeInterface):
    original_thirdparty_sign_in_up = original_implementation.sign_in_up

    async def thirdparty_sign_in_up(
        third_party_id: str,
        third_party_user_id: str,
        email: str,
        oauth_tokens: Dict[str, Any],
        raw_user_info_from_provider: RawUserInfoFromProvider,
        tenant_id: str,
        user_context: Dict[str, Any]
    ) -> SignInUpOkResult:
        existing_users = await get_users_by_email_thirdparty(tenant_id, email, user_context)
        passwordless_user = await get_users_by_email_passwordless(tenant_id, email, user_context)

        if passwordless_user is not None:
            raise Exception("Cannot sign up as email already exists")
        
        if (len(existing_users) == 0):
            # this means this email is new so we allow sign up
            return await original_thirdparty_sign_in_up(third_party_id, third_party_user_id, email, oauth_tokens, raw_user_info_from_provider, tenant_id, user_context)

        is_sign_in = False
        for user in existing_users:
            if user.third_party_info.id == third_party_id and user.third_party_info.user_id == third_party_user_id:
                is_sign_in = True
                break
        
        if is_sign_in:
            return await original_thirdparty_sign_in_up(third_party_id, third_party_user_id, email, oauth_tokens, raw_user_info_from_provider, tenant_id, user_context)

        # this means that the email already exists with another social or passwordless login method.
        # so we throw an error.
        raise Exception("Cannot sign up as email already exists")

    original_implementation.sign_in_up = thirdparty_sign_in_up

    return original_implementation


def override_passwordless_apis(original_implementation: PasswordlessAPIInterface):
    original_create_code_post = original_implementation.create_code_post

    async def create_code_post(email: Union[str, None], phone_number: Union[str, None], tenant_id: str, api_options: PasswordlessAPIOptions,
                               user_context: Dict[str, Any],
                               ):
        if email is not None:
            existing_user = await get_users_by_email_passwordless(tenant_id, email, user_context)

            third_party_existing_users = await get_users_by_email_thirdparty(tenant_id, email, user_context)
            
            if (existing_user is None and len(third_party_existing_users) == 0):
                # this means this email is new so we allow sign up
                return await original_create_code_post(email, phone_number, tenant_id, api_options, user_context)

            return GeneralErrorResponse("Seems like you already have an account with another social login provider. Please use that instead.")

        # phone number based login, so we allow it.
        return await original_create_code_post(email, phone_number, tenant_id, api_options, user_context)

    original_implementation.create_code_post = create_code_post
    return original_implementation

def override_thirdparty_apis(original_implementation: ThirdPartyAPIInterface):
    original_sign_in_up_post = original_implementation.sign_in_up_post

    async def sign_in_up_post(
        provider: Provider,
        redirect_uri_info: Union[RedirectUriInfo, None],
        oauth_tokens: Union[Dict[str, Any], None],
        tenant_id: str,
        api_options: ThirdPartyAPIOptions,
        user_context: Dict[str, Any]
    ):
        try:
            return await original_sign_in_up_post(provider, redirect_uri_info, oauth_tokens, tenant_id, api_options, user_context)
        except Exception as e:
            if str(e) == "Cannot sign up as email already exists":
                return GeneralErrorResponse("Seems like you already have an account with another method. Please use that instead.")
            raise e

    original_implementation.sign_in_up_post = sign_in_up_post
    return original_implementation


init(
    app_info=InputAppInfo(
        api_domain="...", app_name="...", website_domain="..."),
    framework='...',  
    recipe_list=[
        passwordless.init(
            contact_config=...,  
            flow_type="...",  
            override=passwordless.InputOverrideConfig(
                apis=override_passwordless_apis,
            ),
        ),
        thirdparty.init(
            override=thirdparty.InputOverrideConfig(
                apis=override_thirdparty_apis,
                functions=override_thirdparty_functions
            )
        )
    ]
)

In the above code snippet, we override the signInUpPOST (third party recipe) and the createCodePOST (passwordless recipe) API as well as the signInUp recipe function.

The signInUpPOST API is called by the frontend after the user is redirected back to your app from the third party provider's login page. The API then exchanges the auth code with the provider and calls the signInUp function with the user's email and thirdParty info.

The createCodePOST API is called when the user enters their email, or phone number during passwordless login. This API generates the passwordless OTP / link and sends it to the user's email / phone.

We override the signInUp recipe function to:

• Get all ThirdParty or Passwordless users that have the same input email.
• If no users exist with that email, it means that this is a new email and so we call the originalImplementation function which creates a new user.
• If instead, a user exists, but has the same thirdPartyId and thirdPartyUserId, implying that this is a sign in (for example a user who had signed up with Google is signing in with Google), we again allow the operation by calling the originalImplementation function.
• If neither of the conditions above match, it means that the user is trying to sign up with a third party provider whilst they already have an account with another provider or via passwordless login. So here we throw an error with some custom message.

Finally, we override the signInUpPOST API to catch that custom error and return a general error status to the frontend with a message that will be displayed to the user in the sign in form.

We also override the createCodePOST API to perform similar checks:

• If the input is phone number based, then we call the originalImplementation function allowing sign up or sign in. This is OK since social login is always email based, so there is no scope of duplication.
• Otherwise, we det all ThirdParty or Passwordless users that have the same input email.
• If no users exist with that email, it means that this is a new email and so we call the originalImplementation function which creates a new user.
• Else we check if the existing user is not a Third Party login user, implying that it's a Passwordless login user. So here, we also call the originalImplementation function to allow the user to sign in.
• If neither of the conditions above match, it means that the user is trying to sign up with passwordless login whilst they already have an account with a third party provider. So here we return an appropriate message to be displayed on the frontend.

Multi Tenancy

For a multi tenant setup, the customisations above ensure that multiple accounts with the same email don't exist within a single tenant. If you want to ensure that there is no duplication across all tenants, then when fetching the list of existing users, you should loop through all tenants in your app, which you can fetch by using the listAllTenants function of the multi tenancy recipe.