Azure AD B2C add user using Graph API with custom user attributes C#

Question

I'm using the MS Graph API to register user on AD B2C, and it works when I tried without adding additional user attributes, but it fails with an error

properties are not available

when I tried adding those user custom attributes.

I did followed other solution thread and added clientid without '-' while setting attribute name in dictionary but doesn't work.

Here is my code snippet:

public class UserService : IUserService
{
    private readonly ILogger<UserService> logger;
    private readonly GraphServiceClient graphServiceClient;
    private readonly string[] supportedRegionCodes;
    private readonly string  _clientId;

    public UserService(ILogger<UserService> logger, IOptions<B2CConfiguration> options)
    {
        this.logger = logger;

        ClientSecretCredentialOptions credentialOptions = new()
        {
            AuthorityHost = AzureAuthorityHosts.AzurePublicCloud,
        };

        ClientSecretCredential clientSecretCredential = new(
            options.Value.TenantId,
            options.Value.ClientId,
            options.Value.ClientSecret,
            credentialOptions);

        _clientId = options.Value.ClientId;

        this.graphServiceClient = new GraphServiceClient(clientSecretCredential, options.Value.Scopes);
        this.supportedRegionCodes = options.Value.SupportedRegionCodes;
    }

    public async Task<string?> RegisterUserToB2C(object userDetails)
    {
        try
        {
            string clientId = _clientId.Replace("-", string.Empty);
            var user = new User
            {
                Identities = new List<ObjectIdentity>
                {
                    new ObjectIdentity
                    {
                        SignInType = "userName",
                        Issuer ="empxxxqa.onmicrosoft.com",
                        IssuerAssignedId = "testuser011"
                    }
                },

                DisplayName = "Test User",
                GivenName = "Test",       
                Surname = "User",
                Mail = "[email protected]",
                OtherMails = new List<string> { "[email protected]" },
                PasswordProfile = new PasswordProfile
                {
                    Password = "@w0rd123!",
                    ForceChangePasswordNextSignIn = true
                },
                UserType = "Member",
                AdditionalData = new Dictionary<string, object>
                    {
                        {$"extension_{clientId}_CardId","TEST"}
                    }
            };

            var created = await graphServiceClient.Users.PostAsync(user);

            return created?.Id;
        }
        catch (Exception ex)
        {
            return ex.Message;
        }
    }
}

This is the error I'm getting:

The following extension properties are not available: extension_3a84xxxxxxxxxxx126f_CardId.

I've also added a screenshot of the property we created in b2c:

I'm relatively new to AD B2C and MS Graph API, do I need to add any thing at the B2C level? As without additional custom user attributes, when I tried to register, it worked, so I believe there should be no permission issues that causing it.

What is the client ID you are passing in extension_3a84xxxxxxxxxxx126f_CardId? — Rukmini
– Rukmini, Commented Apr 28 at 11:48
@Rukmini , i was passing registered app's client id in that, will try with b2c-extension-app client id — Dark S
– Dark S, Commented Apr 28 at 14:33

Rukmini · Accepted Answer · 2025-04-28 12:51:57Z

To create user using Microsoft Graph API with custom user attributes C#, check the below:

I created a custom user attribute:

enter image description here

Note that: You need to pass Client ID of b2c-extensions-app without hyphen as the Extension ID like below:

enter image description here

extension_<b2cExtensionsAppIDwithouthyphen>_CardId

Now for sample, I used the below code to create user with custom user attribute in Azure AD B2C:

namespace GraphAPIConsoleApp
{
    class Program
    {
        static async Task Main(string[] args)
        {
            // Azure AD B2C credentials
            string tenantId = "TenantID";
            string clientId = "ClientID";
            string clientSecret = "Secret";
            string userSignIn = "testuser011"; // Example user identifier

            // Initialize GraphServiceClient with client credentials
            var clientSecretCredential = new ClientSecretCredential(tenantId, clientId, clientSecret);
            var graphClient = new GraphServiceClient(clientSecretCredential);

            // Create the user with custom extension attribute
            var user = new User
            {
                DisplayName = "Test User",
                GivenName = "Test",
                Surname = "User",
                Mail = "[email protected]",
                OtherMails = new List<string> { "[email protected]" },
                PasswordProfile = new PasswordProfile
                {
                    Password = "@w0rd123!",
                    ForceChangePasswordNextSignIn = true
                },
                UserType = "Member",
                Identities = new List<ObjectIdentity>
                {
                    new ObjectIdentity
                    {
                        SignInType = "userName",
                        Issuer = "infrab2c.onmicrosoft.com", // Change to your B2C domain
                        IssuerAssignedId = "testuser011"
                    }
                },
                // Add custom extension attribute
                AdditionalData = new Dictionary<string, object>
                {
                    { $"extension_<b2cExtensionsAppIDwithouthyphen>_CardId", "123" }
                }
            };

            try
            {
                // Create the user in Azure AD B2C
                var createdUser = await graphClient.Users.PostAsync(user);
                Console.WriteLine($"User created with ID: {createdUser.Id}");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error creating user: {ex.Message}");
            }
        }
    }
}

enter image description here

User created successfully:

enter image description here

To verify whether the custom user attribute I ran the user flow and can see the custom user attribute in ID token successfully:

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