Azure访问控制服务（ACS）与认证具体操作
S2S trust with ACS.
在SharePoint 混合信任认证时，需要在服务器上创建S2S信任。也就是三方信任。SharePoint， SharePoint online 和Azsure AD。
也顺便提一下，这里说的SharePoint 是 SharePoint on-premise.
操作步骤如下，
1，S2S Trust relationship needs to be created.
2，Trust between SharePoint on-premises farm,SharePoint online and Azure AD
3, SPO uses Azure AD as a trusted token singing service.
4, S2S auth configuration done through the hybrid picker wizard.
5, S2S auth can be configuraed via powershell
- required for -
- Hybried Search
- Hybrid BCS
- Hybrid sites features
- Hybrid taxonomy(preview)
上面内容提到混合搜索，Hybried Search，这个功能是什么那？
1，Hybrid Search
- important prerequisite for hybrid search.
- Users can query SharePoint Online index from on-premises.
- Users can query on-premises content from within SharePoint online.
上面这两句废话是，用户可以使用本地版查找Sharepoint online 场，反过来也一样，可以使用online 查找本地服务器场。
2， Search Queries
- Search Request is sent with users UPN.
- UPN is used to look up identity of the user in SPO user profile store.
- If match found, user identity is regenerated in the cloud.
- used to perform security trimming of search results.
证书，这里很重要，我简单解释一下，在SharePoint 已经有一个证书了。这里被当作STS 使用，是一个安全令牌的服务证书。
- SharePoint on-premises has its own self signed certs.
- Validates incoming tokens.
- In hybrid, Azure AD is trusted token signing service for SPO.
- Uses SP on-premises STS certificate as the signing certificate.
- Use your existing SharePoint on-premises STS certificate.
- Or create your own ertificate.
- Can be self signed.
- Do not reuse the certificate.
配置S2S 信任方法：
Post Install：
after the S2S trust,
- Security tokens issued by Azure AD are trusted by SharePoint Online and on-premises.
- SharePoint online registered as a high-trust application in sharePoint on-premises.
- Users are granted access based on security tokens.
- Tokens are used by authentication services in both online and on-prem
总之，SP，SPO 和S2S，在混合使用非常重要，也是无缝集成的，