Different link for Identity Provider for MFA authentication

##### ISSUE TYPE

* Improvement Request

##### COMPONENT NAME

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Core
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##### CLOUDSTACK VERSION

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4.17.2
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##### CONFIGURATION

It would be great to have the possibility of customizing the FQDN of identity provider link per domain for MFA.
We don't need to have multiple platforms connected to CS, just to have the possibility of configure a sort of cname.

For example: for "Society one" having authentication.societyone.com and for "Society two" having authentication.societytwo.com

##### OS / ENVIRONMENT

CentOS 7

##### SUMMARY

##### STEPS TO REPRODUCE

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##### EXPECTED RESULTS

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##### ACTUAL RESULTS

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It is not possible actually to have a different link for MFA
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先定位 CloudStack 的 MFA identity-provider 連結處理邏輯及其網域設定入口。定義每個網域應如何設定 FQDN 或 CNAME 值，並驗證每個網域都會產生其預期的 MFA 連結；issue 未指定任何測試或檔案。

由索引模型根據 Issue 內容生成。