Title : Custom authentication extensions , Retrieve and return data from an OnAttributeCollectionStart event . Here the Email Address is not Coming Why ?

Hi I am implementing the Custom authentication extensions . In Retrieve and return data from an OnAttributeCollectionStart event this is the sample payload which is coming {

"type": "microsoft.graph.authenticationEvent.attributeCollectionStart",

"source": "/tenants/aaaabbbb-0000-cccc-1111-dddd2222eeee/applications/<resourceAppguid>",

"data": {

"@odata.type": "microsoft.graph.onAttributeCollectionStartCalloutData",

"tenantId": "aaaabbbb-0000-cccc-1111-dddd2222eeee",

"authenticationEventListenerId": "00001111-aaaa-2222-bbbb-3333cccc4444",

"customAuthenticationExtensionId": "11112222-bbbb-3333-cccc-4444dddd5555",

"authenticationContext": {

    "correlationId": "<GUID>",

    "client": {

        "ip": "30.51.176.110",

        "locale": "en-us",

        "market": "en-us"

    },

    "protocol": "OAUTH2.0",

    "clientServicePrincipal": {

        "id": "<Your Test Applications servicePrincipal objectId>",

        "appId": "<Your Test Application App Id>",

        "appDisplayName": "My Test application",

        "displayName": "My Test application"

    },

    "resourceServicePrincipal": {

        "id": "<Your Test Applications servicePrincipal objectId>",

        "appId": "<Your Test Application App Id>",

        "appDisplayName": "My Test application",

        "displayName": "My Test application"

    }

},

"userSignUpInfo": {

  "attributes": {

    "givenName": {

      "@odata.type": "microsoft.graph.stringDirectoryAttributeValue",

      "value": "Larissa Price",

      "attributeType": "builtIn"

    },

    "companyName": {

      "@odata.type": "microsoft.graph.stringDirectoryAttributeValue",

      "value": "Contoso University",

      "attributeType": "builtIn"

    },

    "extension_<appid>_universityGroups": {

      "@odata.Type": "microsoft.graph.stringDirectoryAttributeValue",

      "value": "Alumni,Faculty",

      "attributeType": "directorySchemaExtension"

    },

    "extension_<appid>_graduationYear": {

      "@odata.type": "microsoft.graph.int64DirectoryAttributeValue",

      "value": 2010,

      "attributeType": "directorySchemaExtension"

    },

    "extension_<appid>_onMailingList": {

      "@odata.type": "microsoft.graph.booleanDirectoryAttributeValue",

      "value": false,

      "attributeType": "directorySchemaExtension"

    }

  },

  "identities": [

    {

      "signInType": "email",

      "issuer": "contoso.onmicrosoft.com",

      "issuerAssignedId": "******@contoso.onmicrosoft.com"

    }

  ]

}

}

} Here Why the Email Address is not coming in the Attribute Section . Because in my External Tenant , In custom Attributes it is defining defaultly.But It is not ccoming in the response. So Is there any way to fetch the Email Address (Actual Email Address not Issuer Assigned ID or UPN ) of the user ?