Sign-up and sign-in with Imgur using Azure AD B2C

using System;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;
using System.Web.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.Extensions.Logging;

namespace SignInWithImgur
{
    public static class GetImgurClaims
    {
        private static readonly HttpClient InnerClient = new HttpClient();

        [FunctionName("GetImgurClaims")]
        public static async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Anonymous, "get")] HttpRequest request,
            ILogger logger)
        {
            if (!request.Headers.TryGetValue("Authorization", out var authorizationHeaderValues))
            {
                logger.LogError("The Authorization header is missing");
                return new BadRequestResult();
            }

            if (authorizationHeaderValues.Count > 1)
            {
                logger.LogError("The Authorization header is invalid");
                return new BadRequestResult();
            }

            var authorizationHeaderValue = authorizationHeaderValues[0];
            var authorizationHeaderValueParts = authorizationHeaderValue.Split(' ');

            if (authorizationHeaderValueParts.Length != 2 || !authorizationHeaderValueParts[0].Equals("Bearer", StringComparison.OrdinalIgnoreCase))
            {
                logger.LogError("The Authorization header is invalid");
                return new BadRequestResult();
            }

            var innerRequest = new HttpRequestMessage(HttpMethod.Get, "https://api.imgur.com/3/account/me");
            innerRequest.Headers.Authorization = new AuthenticationHeaderValue(authorizationHeaderValueParts[0], authorizationHeaderValueParts[1]);
            var innerResponse = await InnerClient.SendAsync(innerRequest);

            if (innerResponse.StatusCode != HttpStatusCode.OK)
            {
                return new InternalServerErrorResult();
            }

            var innerResponseModel = await innerResponse.Content.ReadAsJsonAsync<ImgurClaimsResponseModel>();

            var responseModel = new
            {
                id = innerResponseModel.Data?.Id
            };

            return new OkObjectResult(responseModel);
        }
    }
}

using Newtonsoft.Json;

namespace SignInWithImgur
{
    public class ImgurClaimsResponseModel
    {
        [JsonProperty(PropertyName = "data")]
        public ImgurAccountModel Data { get; set; }
    }

    public class ImgurAccountModel
    {
        [JsonProperty("id")]
        public string Id { get; set; }
    }
}

using System.Net.Http;
using System.Threading.Tasks;
using Newtonsoft.Json;

namespace SignInWithImgur
{
    public static class HttpContentExtensions
    {
        public static async Task<T> ReadAsJsonAsync<T>(this HttpContent content)
        {
            if (content == null)
            {
                return default;
            }

            var value = await content.ReadAsStringAsync();
            return JsonConvert.DeserializeObject<T>(value);
        }
    }
}

<ClaimsProvider>
  <Domain>imgur.com</Domain>
  <DisplayName>Imgur</DisplayName>
  <TechnicalProfiles>
    <TechnicalProfile Id="Imgur-OAuth2">
      <DisplayName>Imgur</DisplayName>
      <Protocol Name="OAuth2" />
      <Metadata>
        <Item Key="client_id">your-imgur-client-id</Item>
        <Item Key="authorization_endpoint">https://api.imgur.com/oauth2/authorize</Item>
        <Item Key="AccessTokenEndpoint">https://api.imgur.com/oauth2/token</Item>
        <Item Key="ClaimsEndpoint">https://your-function-app-name.azurewebsites.net/api/GetImgurClaims</Item>
        <Item Key="HttpBinding">POST</Item>
        <Item Key="BearerTokenTransmissionMethod">AuthorizationHeader</Item>
        <Item Key="UsePolicyInRedirectUri">false</Item>
      </Metadata>
      <CryptographicKeys>
        <Key Id="client_secret" StorageReferenceId="B2C_1A_ImgurClientSecret" />
      </CryptographicKeys>
      <OutputClaims>
        <OutputClaim ClaimTypeReferenceId="authenticationSource" DefaultValue="socialIdpAuthentication" AlwaysUseDefaultValue="true" />
        <OutputClaim ClaimTypeReferenceId="identityProvider" DefaultValue="imgur.com" AlwaysUseDefaultValue="true" />
        <OutputClaim ClaimTypeReferenceId="issuerUserId" PartnerClaimType="id" />
      </OutputClaims>
      <OutputClaimsTransformations>
        <OutputClaimsTransformation ReferenceId="CreateRandomUPNUserName" />
        <OutputClaimsTransformation ReferenceId="CreateUserPrincipalName" />
        <OutputClaimsTransformation ReferenceId="CreateAlternativeSecurityId" />
      </OutputClaimsTransformations>
      <UseTechnicalProfileForSessionManagement ReferenceId="SM-SocialLogin" />
    </TechnicalProfile>
  </TechnicalProfiles>
</ClaimsProvider>

<OrchestrationStep Order="1" Type="CombinedSignInAndSignUp" ContentDefinitionReferenceId="api.signuporsignin">
  <ClaimsProviderSelections>
    ...
    <ClaimsProviderSelection TargetClaimsExchangeId="ImgurExchange" />
  </ClaimsProviderSelections>
  ...
</OrchestrationStep>

<OrchestrationStep Order="2" Type="ClaimsExchange">
  ...
  <ClaimsExchanges>
    <ClaimsExchange Id="ImgurExchange" TechnicalProfileReferenceId="Imgur-OAuth2" />
  </ClaimsExchanges>
  ...
</OrchestrationStep>

<RelyingParty>
  <DefaultUserJourney ReferenceId="ImgurSignUpSignIn" />
  ...
</RelyingParty>