owa安装完后，在sharepoint网站上打开word，excel，报错，Sorry, something went wrong, 通过correlation id找到错误信息（如何在sharepoint里通过correlation id查找详细的错误信息）：
Area : SharePoint Foundation
Category : WOPI
Level : Unexpected
EventID : ajc39
Message : WOPIFrame - Unhandled exception: System.NotSupportedException: Can not create an identity context for system account user token.
at Microsoft.SharePoint.IdentityModel.SPIdentityContext.Create(SPUserToken token, Boolean isShareByLinkGuestUser) at Micr
osoft.SharePoint.IdentityModel.SPIdentityContext.Create(SPUser user) at Microsoft.SharePoint.IdentityModel.OAuth2.SPOAuth2Sec
urityTokenManager.IssueLoopbackTokenString(Uri endpointAddress, SPUser user, String applicationContext, DateTime& validTo) at
Microsoft.SharePoint.Utilities.SPWOPIHost.GetAccessToken(SPWeb web, Guid uniqueId, String proofKeyId, SPUrlZone zone, SPBasePerm
issions perms, Boolean hasEditLicense, Int64& ttl) at Microsoft.SharePoint.Utilities.SPWOPIHost.GetAccessToken(SPFile file, S
tring proofKeyId, SPUrlZon...
发现不能用system account， 于是换了用户登录，页面上还是不能正常priview， 最终重新run下面的power shell命令解决：
# New-OfficeWebAppsFarm -InternalUrl $interalURL -ExternalUrl $externalURL -SSLOffloaded -EditingEnabled New-OfficeWebAppsFarm -InternalUrl $interalURL -AllowHttp -EditingEnabled