Hi @Michael Lau ,
Thanks for reaching out.
Azure AD B2C allow you to pass "login_hint" query string parameter to the OpenID Connect authentication request which allow to automatically populates the sign-in name, while the user only needs to provide the password.
For a custom policy, you can add the login_hint by adding the "DefaultValue" attribute to the "signInName" input claim for the "SelfAsserted-LocalAccountSignin-Email" technical profile as :
<ClaimsProvider>
<DisplayName>Local Account</DisplayName>
<TechnicalProfiles>
<TechnicalProfile Id="SelfAsserted-LocalAccountSignin-Email">
<InputClaims>
<!-- Add the login hint value to the sign-in names claim type -->
<InputClaim ClaimTypeReferenceId="signInName" DefaultValue="{OIDC:LoginHint}" />
</InputClaims>**
</TechnicalProfile>
</TechnicalProfiles>
</ClaimsProvider>
Reference: https://learn.microsoft.com/en-us/azure/active-directory-b2c/direct-signin?pivots=b2c-custom-policy
Hope this will help.
Thanks,
Shweta
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