In a B2C custom profile I can't get a custom claim to populate with the user's groups - azure

Question

I've followed the detailed advice here to add a custom policy to my Azure B2C service which is designed to populate a groups claim via an API during the authentication flow.
I've built this on top of a fresh B2C instance and apart from my modifications, the custom policies are those available in the Azure sample here. I'm just using the local accounts sample and my modifications target the SignUpOrSignIn custom policy. For now, all my changes are in the TrustFrameworkBase.xml file.
When I test the policy via the portal with a redirect URI set to https://jwt.ms/ my resultant token does not include a groups claim at all. However, via Application Insights I can see my REST api being called with the correct parameter and according to its logs is successfully loading the user groups and returning the expected result.
Is there anything obvious I'm doing wrong here? This is the user journey I've changed:
<UserJourney Id="SignUpOrSignIn">
<OrchestrationSteps>
<OrchestrationStep Order="1" Type="CombinedSignInAndSignUp" ContentDefinitionReferenceId="api.signuporsignin">
<ClaimsProviderSelections>
<ClaimsProviderSelection ValidationClaimsExchangeId="LocalAccountSigninEmailExchange" />
</ClaimsProviderSelections>
<ClaimsExchanges>
<ClaimsExchange Id="LocalAccountSigninEmailExchange" TechnicalProfileReferenceId="SelfAsserted-LocalAccountSignin-Email" />
</ClaimsExchanges>
</OrchestrationStep>
<OrchestrationStep Order="2" Type="ClaimsExchange">
<Preconditions>
<Precondition Type="ClaimsExist" ExecuteActionsIf="true">
<Value>objectId</Value>
<Action>SkipThisOrchestrationStep</Action>
</Precondition>
</Preconditions>
<ClaimsExchanges>
<ClaimsExchange Id="SignUpWithLogonEmailExchange" TechnicalProfileReferenceId="LocalAccountSignUpWithLogonEmail" />
</ClaimsExchanges>
</OrchestrationStep>
<!-- This step reads any user attributes that we may not have received when in the token. -->
<OrchestrationStep Order="3" Type="ClaimsExchange">
<ClaimsExchanges>
<ClaimsExchange Id="AADUserReadWithObjectId" TechnicalProfileReferenceId="AAD-UserReadUsingObjectId" />
</ClaimsExchanges>
</OrchestrationStep>
<OrchestrationStep Order="4" Type="ClaimsExchange">
<ClaimsExchanges>
<ClaimsExchange Id="GetUserGroups" TechnicalProfileReferenceId="GetUserGroups" />
</ClaimsExchanges>
</OrchestrationStep>
<OrchestrationStep Order="5" Type="SendClaims" CpimIssuerTechnicalProfileReferenceId="JwtIssuer" />
</OrchestrationSteps>
<ClientDefinition ReferenceId="DefaultWeb" />
</UserJourney>
My only change here was to change the order of the SendClaims step to 5 and add a new step 4. This references a GetUserGroups technical profile which I added at the end of the technical profiles under the "Azure Active Directory" claims provider (I wasn't sure if this was correct). It looks like this:
<TechnicalProfile Id="GetUserGroups">
<DisplayName>Retrieves security groups assigned to the user</DisplayName>
<Protocol Name="Proprietary" Handler="Web.TPEngine.Providers.RestfulProvider, Web.TPEngine, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
<Metadata>
<Item Key="ServiceUrl">https://<redacted>.azurewebsites.net/api/UserGroups?code=<auth-code></Item>
<Item Key="AuthenticationType">None</Item>
<Item Key="SendClaimsIn">QueryString</Item>
<Item Key="AllowInsecureAuthInProduction">true</Item>
</Metadata>
<InputClaims>
<InputClaim Required="true" ClaimTypeReferenceId="objectId" />
</InputClaims>
<OutputClaims>
<OutputClaim ClaimTypeReferenceId="groups" />
</OutputClaims>
<UseTechnicalProfileForSessionManagement ReferenceId="SM-Noop" />
</TechnicalProfile>
The service URL is an Azure function which accepts a user object Id as objectId query parameters and returns the follow JSON:
{"groups":["b1cc6d36-ac97-420a-8a9a-58a7be4aff36","71fa71e1-7edd-48a7-a147-16705c856cb0"]}
If anyone can point me in the right direction I'd be grateful.

Answer 1

Turns out there was one crucial thing I was missing that wasn't referenced in the guide I was following. I found the answer here. Having retrieved the claim value from my REST API I needed to configure the custom policy to include the claim:
<RelyingParty>
<DefaultUserJourney ReferenceId="SignUpOrSignIn" />
<TechnicalProfile Id="PolicyProfile">
<DisplayName>PolicyProfile</DisplayName>
<Protocol Name="OpenIdConnect" />
<OutputClaims>
<OutputClaim ClaimTypeReferenceId="displayName" />
<OutputClaim ClaimTypeReferenceId="givenName" />
<OutputClaim ClaimTypeReferenceId="surname" />
<OutputClaim ClaimTypeReferenceId="email" />
<OutputClaim ClaimTypeReferenceId="objectId" PartnerClaimType="sub"/>
<OutputClaim ClaimTypeReferenceId="tenantId" AlwaysUseDefaultValue="true" DefaultValue="{Policy:TenantObjectId}" />
<OutputClaim ClaimTypeReferenceId="groups" DefaultValue="" />
</OutputClaims>
<SubjectNamingInfo ClaimType="sub" />
</TechnicalProfile>
</RelyingParty>