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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首先定位 CloudStack 的 MFA identity-provider 链接处理逻辑及其域配置入口。定义每个域应如何配置 FQDN 或 CNAME 值，并验证每个域都会生成其预期的 MFA 链接；issue 未指定任何测试或文件。

由索引模型根据 Issue 内容生成。