How to direct B2C Federated user to Microsoft common login endpoint - angularjs

Question

I am using Azure AD B2C and have added sign in/sign up with custom templates and policies. I am using msal.js on the frontend.
When any user tries to login to our application, we have process to know if the domain is already federated with Microsoft B2C. Once we identify the user, we want to direct the user to Microsoft common login endpoint by passing the login_hint, so that they are forced to use work account and get the id_token.
I am trying to get the endpoint working (need to pass login_hint, don't know how)
directauthority ="https://login.microsoftonline.com/common/oauth2/authorize?"+ this.Config.signUpSignInPolicy;
clientApplication = new Msal.UserAgentApplication(
this.tenantConfig.clientID, this.directauthority,
);
I got an error "endpoints_resolution_error:Endpoints cannot be resolved"
How can I resolve this?
Please suggest
Thanks,

Answer 1

You can add the "domain_hint" and "login_hint" parameters to the Azure AD B2C request:
https://login.microsoftonline.com/<tenant>/oauth2/v2.0/authorize?p=<policy>&...&domain_hint=onmicrosoft.com&login_hint=me#contoso.com
If you set the "domain_hint" parameter to the Azure AD technical profile's <Domain /> value, then Azure AD B2C will redirect to the Azure AD endpoint without showing the sign-up or sign-in page to the end user.
To pass the "login_hint" parameter through from Azure AD B2C to the Azure AD endpoint:
1) Create a "loginHint" claim type:
<BuildingBlocks>
<ClaimsSchema>
<ClaimType Id="loginHint">
<DisplayName>Login Hint</DisplayName>
<DataType>string</DataType>
</ClaimType>
</ClaimsSchema>
</BuildingBlocks>
2) Add the "loginHint" input claim to the Azure AD technical profile:
<ClaimsProviders>
<ClaimsProvider>
<Domain>onmicrosoft.com</Domain>
<DisplayName>Work Account</DisplayName>
<TechnicalProfiles>
<TechnicalProfile Id="WorkProfile">
<DisplayName>Work Profile</DisplayName>
<Protocol Name="OpenIdConnect"/>
<OutputTokenFormat>JWT</OutputTokenFormat>
<Metadata>
...
</Metadata>
<CryptographicKeys>
...
</CryptographicKeys>
<InputClaims>
<InputClaim ClaimTypeReferenceId="loginHint" PartnerClaimType="login_hint" DefaultValue="{OIDC:LoginHint}" />
</InputClaims>
<OutputClaims>
...
</OutputClaims>
<OutputClaimsTransformations>
...
</OutputClaimsTransformations>
<UseTechnicalProfileForSessionManagement ReferenceId="SM-Noop" />
</TechnicalProfile>
</TechnicalProfiles>
</ClaimsProvider>
</ClaimsProviders>
The "loginHint" input claim references a claims resolver that sets this input claim value to the "login_hint" parameter of the Azure AD B2C request.