In the PhoneFactor-InputOrVerify Technical Profile (B2C custom user flow), is it possible to allow the user to change their default mobile number? - azure

Question

In Azure B2C custom policies, our business process requirements mean we need control over whether:
The user may not replace the mobile number we have on record for them (i.e. first-time password set experience), or
We present the number we hold on record for them by default, but allow the user to overtype and save this number with a new number (e.g. logged-in edit profile experience).
The question: Is there a way I can allow the user to replace the number we hold on record for them with a new number, perhaps by the addition of a new button [Provide New Number] in this series:
[Send Code] [Call Me] [New Button To Provide New Number] [Cancel]
PhoneFactor-InputOrVerify sample screen (image)
The code below is a slight modification of the similarly-named policy from the B2C Custom Policy Starterpack.
Note how in this example we're providing the mobile phone number value stored in the mobile property of the user object as strongAuthenticationNumber. This is because there is currently no way of setting the MFA number programmatically. (Thanks for your help, Chris Padgett.)
Other than this, the policy is as per starterpack.
<ClaimsProvider>
<DisplayName>PhoneFactor</DisplayName>
<TechnicalProfiles>
<TechnicalProfile Id="PhoneFactor-InputOrVerify">
<DisplayName>PhoneFactor</DisplayName>
<Protocol Name="Proprietary" Handler="Web.TPEngine.Providers.PhoneFactorProtocolProvider, Web.TPEngine, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
<Metadata>
<Item Key="ContentDefinitionReferenceId">api.phonefactor</Item>
<Item Key="ManualPhoneNumberEntryAllowed">true</Item>
</Metadata>
<CryptographicKeys>
<Key Id="issuer_secret" StorageReferenceId="B2C_1A_TokenSigningKeyContainer" />
</CryptographicKeys>
<InputClaimsTransformations>
<InputClaimsTransformation ReferenceId="CreateUserIdForMFA" />
</InputClaimsTransformations>
<InputClaims>
<InputClaim ClaimTypeReferenceId="userIdForMFA" PartnerClaimType="UserId" />
<!--InputClaim ClaimTypeReferenceId="strongAuthenticationPhoneNumber" /-->
<InputClaim ClaimTypeReferenceId="mobile" PartnerClaimType="strongAuthenticationPhoneNumber" />
</InputClaims>
<OutputClaims>
<OutputClaim ClaimTypeReferenceId="Verified.strongAuthenticationPhoneNumber" PartnerClaimType="Verified.OfficePhone" />
<OutputClaim ClaimTypeReferenceId="newPhoneNumberEntered" PartnerClaimType="newPhoneNumberEntered" />
</OutputClaims>
<UseTechnicalProfileForSessionManagement ReferenceId="SM-MFA" />
</TechnicalProfile>
</TechnicalProfiles>
</ClaimsProvider>
I suspect there may be some metadata setting to enable a button or text input box as described, but to my knowledge there is no documentation for this yet.

Answer 1

You must create a custom flow for this that:
Prompts the end user to sign in with a local or external account.
Reads the current phone number for the end user from Azure AD.
Prompts the end user to verify their current phone number.
Prompts the end user to enter and verify their new phone number.
Writes the new phone number for the end user to Azure AD.
See this sample policy.