B2C是否有一种从外部身份提供者中提取表单提交字段的方式？

是的，B2C提供了一种方式，可以从外部身份提供者中提取表单提交字段。这种方式使用自定义策略，通过在策略中添加自定义的TechnicalProfile来实现。

以下是一个示例代码，展示了如何从外部身份提供者中提取表单提交字段：

<ClaimsProviders>
  <ClaimsProvider>
    <DisplayName>External Identity Provider</DisplayName>
    <TechnicalProfiles>
      <TechnicalProfile Id="ExternalIdpProfile">
        <DisplayName>External Identity Provider</DisplayName>
        <Protocol Name="OpenIdConnect" />
        <OutputTokenFormat>JWT</OutputTokenFormat>
        <Metadata>
          <!-- External IdP metadata here -->
        </Metadata>
        <CryptographicKeys>
          <!-- Cryptographic keys for External IdP here -->
        </CryptographicKeys>
        <InputClaims>
          <!-- Input claims for External IdP here -->
        </InputClaims>
        <OutputClaims>
          <!-- Output claims from External IdP here -->
        </OutputClaims>
      </TechnicalProfile>
    </TechnicalProfiles>
  </ClaimsProvider>
</ClaimsProviders>

<BuildingBlocks>
  <ClaimsSchema>
    <ClaimType Id="externalField">
      <DisplayName>External Field</DisplayName>
      <DataType>string</DataType>
    </ClaimType>
  </ClaimsSchema>
</BuildingBlocks>

<ClaimsTransformations>
  <ClaimsTransformation Id="ExtractExternalField" TransformationMethod="RegexMatch">
    <InputClaims>
      <InputClaim ClaimTypeReferenceId="externalField" TransformationClaimType="inputClaim" />
    </InputClaims>
    <InputParameters>
      <InputParameter Id="pattern">@(\d+)</InputParameter>
    </InputParameters>
    <OutputClaims>
      <OutputClaim ClaimTypeReferenceId="externalField" TransformationClaimType="outputClaim" />
    </OutputClaims>
  </ClaimsTransformation>
</ClaimsTransformations>

<RelyingParty>
  <DefaultUserJourney />
  <UserJourneys>
    <UserJourney Id="SignUp">
      <OrchestrationSteps>
        <OrchestrationStep Order="1" Type="ClaimsExchange">
          <Preconditions>
            <Precondition Type="ClaimEquals" ExecuteActionsIf="false">
              <Value>authenticationSource</Value>
              <Value>ExternalIdpProfile</Value>
              <Action>SkipThisOrchestrationStep</Action>
            </Precondition>
          </Preconditions>
          <ClaimsExchanges>
            <ClaimsExchange Id="ExternalIdpExchange" TechnicalProfileReferenceId="ExternalIdpProfile" />
          </ClaimsExchanges>
        </OrchestrationStep>
        <OrchestrationStep Order="2" Type="ClaimsExchange">
          <Preconditions>
            <Precondition Type="ClaimEquals" ExecuteActionsIf="true">
              <Value>authenticationSource</Value>
              <Value>ExternalIdpProfile</Value>
              <Action>SkipThisOrchestrationStep</Action>
            </Precondition>
          </Preconditions>
          <ClaimsExchanges>
            <ClaimsExchange Id="ExtractExternalFieldExchange" TechnicalProfileReferenceId="SelfAsserted-ExtractExternalField" />
          </ClaimsExchanges>
        </OrchestrationStep>
        <!-- Other orchestration steps here -->
      </OrchestrationSteps>
    </UserJourney>
  </UserJourneys>
</RelyingParty>

<TechnicalProfile Id="SelfAsserted-ExtractExternalField">
  <DisplayName>Extract External Field</DisplayName>
  <Protocol Name="Proprietary" Handler="Web.TPEngine.Providers.ClaimsTransformationProtocolProvider, Web.TPEngine, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
  <Metadata>
    <Item Key="IncludeClaimResolvingInClaimsHandling">true</Item>
  </Metadata>
  <InputClaims>
    <InputClaim ClaimTypeReferenceId="externalField" />
  </InputClaims>
  <OutputClaims>
    <OutputClaim ClaimTypeReferenceId="externalField" />
  </OutputClaims>
  <OutputClaimsTransformations>
    <OutputClaimsTransformation ReferenceId="ExtractExternalField" />
  </OutputClaimsTransformations>
</TechnicalProfile>

以上代码示例中，首先定义了一个名为"External Identity Provider"的外部身份提供者。然后，在自定义策略中定义了一个ClaimType来表示外部字段。接着，定义了一个ClaimsTransformation来提取外部字段，并将其放入output claim中。

在用户旅程(UserJourney)中，首先检查身份验证源是否为外部身