Azure AD B2C Sign Up with Email Invitation Does Not Show Sign Up Page

Question

I am incorporating a Sign Up with Email Invitation flow in my project by following this Azure AD B2C sample from microsoft:

https://github.com/azure-ad-b2c/samples/tree/master/policies/invite

For test reasons I am setting the redirect_uri parameter of the invitation URL to https://jwt.ms and my expectation for the workflow is:

1. Clicking on the invite URL takes me to b2clogin
2. Azure B2C validates the ID hint token
3. I land on the Sign Up page with pre-populated values in the ID token hint
4. Upon a successful sign up, I am redirected to https://jwt.ms

My expectation, however, is not met and upon clicking the invite URL, I immediately land on the https://jwt.ms with a JWT token containing the invitation number (more details below) and the object ID (sub) of one of the previously created profiles in AD, plus the standard claims like exp, aud, etc.

I suspect that there is a gap in my understanding of how the invite workflow function. What areas of code/policies should I pay attention and modify to ensure a successful invitation sign up?

Some extra details:

1. I am including an invitation number in the ID token hint and NOT an email, therefore the ReadOnlyEmail is replaced with InvitationNumber throughout the custom policy.
2. I have copied fields from my normal sign up policy to the invitation policy, expecting that he user should be able to sign up with any emails they like as long as it's validated by B2C (hence the "False" is removed from the sample technical profile for invitation sign up)
3. The invitation number is also set as an output claim for my app to process it once the JWT token is received from B2C.
4. The invitation policy uses the same policy base as my normal sign in/up.
5. In the shared policy base, I have added a new claims provider for ID token hint validation next to my normal JwtIssuer which references the signing certificate that my app uses to sign the ID token hint and use it in the last step of the SignUpInvitation user journey. I am not sure this is the right thing, but once I use the JwtIssuer, I get an error in B2C that it cannot verify the signature of ID token hint.
6. The technical profile for sign up is as follows, and it is being called from the user journey:

    <TechnicalProfile Id="LocalAccountSignUpWithInvitationToken">
      <DisplayName>Email signup</DisplayName>
      <Protocol Name="Proprietary" Handler="Web.TPEngine.Providers.SelfAssertedAttributeProvider, Web.TPEngine, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
      <Metadata>
        <Item Key="IpAddressClaimReferenceId">IpAddress</Item>
        <Item Key="ContentDefinitionReferenceId">api.localaccountsignup</Item>
        <Item Key="language.button_continue">Create</Item>
      </Metadata>
      <InputClaimsTransformations>
        <InputClaimsTransformation ReferenceId="CopyInvitationToken" />
      </InputClaimsTransformations>
      <InputClaims>
        <InputClaim ClaimTypeReferenceId="extension_InvitationToken" />
        <InputClaim ClaimTypeReferenceId="email" />
      </InputClaims>
      <OutputClaims>
        <OutputClaim ClaimTypeReferenceId="objectId" />
        <OutputClaim ClaimTypeReferenceId="email" PartnerClaimType="Verified.Email" Required="true" />
        <OutputClaim ClaimTypeReferenceId="newPassword" Required="true" />
        <OutputClaim ClaimTypeReferenceId="reenterPassword" Required="true" />
        <OutputClaim ClaimTypeReferenceId="executed-SelfAsserted-Input" DefaultValue="true" />
        <OutputClaim ClaimTypeReferenceId="authenticationSource" />
        <OutputClaim ClaimTypeReferenceId="newUser" />

        <!-- Optional claims, to be collected from the user -->
        <OutputClaim ClaimTypeReferenceId="givenName" />
        <OutputClaim ClaimTypeReferenceId="surName" />
        <OutputClaim ClaimTypeReferenceId="extension_InvitationToken" />
      </OutputClaims>
      <ValidationTechnicalProfiles>
        <ValidationTechnicalProfile ReferenceId="AAD-UserWriteUsingLogonEmail" />
      </ValidationTechnicalProfiles>
      <UseTechnicalProfileForSessionManagement ReferenceId="SM-AAD" />
    </TechnicalProfile>      

7. The user journey is:

  <UserJourneys>
    <UserJourney Id="SignUpInvitation">
      <OrchestrationSteps>
        <!--Read the input claims from the id_token_hint-->
        <OrchestrationStep Order="1" Type="GetClaims" CpimIssuerTechnicalProfileReferenceId="IdTokenHint_ExtractClaims" />
        <!-- Check if user tries to run the policy without invitation -->
        <OrchestrationStep Order="2" Type="ClaimsExchange">
         <Preconditions>
            <Precondition Type="ClaimsExist" ExecuteActionsIf="true">
              <Value>extension_InvitationToken</Value>
              <Action>SkipThisOrchestrationStep</Action>
            </Precondition>
          </Preconditions>        
          <ClaimsExchanges>
            <ClaimsExchange Id="SelfAsserted-Unsolicited" TechnicalProfileReferenceId="SelfAsserted-Unsolicited"/>
          </ClaimsExchanges>
        </OrchestrationStep>
        <!-- Self-asserted sign-up page -->
        <OrchestrationStep Order="3" Type="ClaimsExchange">
          <ClaimsExchanges>
            <ClaimsExchange Id="LocalAccountSignUpWithInvitationToken" TechnicalProfileReferenceId="LocalAccountSignUpWithInvitationToken"/>
          </ClaimsExchanges>
        </OrchestrationStep>
        <!-- Issue an access token-->
        <OrchestrationStep Order="4" Type="SendClaims" CpimIssuerTechnicalProfileReferenceId="JwtIdTokenHintValidator"/>
      </OrchestrationSteps>
      <ClientDefinition ReferenceId="DefaultWeb"/>
    </UserJourney>
  </UserJourneys>

Answer 1

Change <UseTechnicalProfileForSessionManagement ReferenceId="SM-AAD" /> to <UseTechnicalProfileForSessionManagement ReferenceId="SM-Noop" />. You are skipping the page due to SSO it seems.

https://github.com/azure-ad-b2c/samples/blob/master/policies/invite/policy/SignUpInvitation.xml#L100