[BUG] AAD B2C cannot complete well know metadata acquisition through Issuer.

[ZhuXiaoBing-cn]

Describe the bug
The access token obtained by UserFlow at the AAD B2C Endpoint has two cases,
The first kind, the access token of the issuer is https://xxxx.b2clogin.com/tenant-id/v2.0/, this issuer is unable to get a list of metadata by splicing well known.

In the second, the access token issuer is https://xxxx.b2clogin.com/tfp/tenant-id/user-flow-name/v2.0/, this issuer can obtain metadata by splicing well known.

So the user is now throwing an exception in the first case, causing the process to stop moving forward.

[ZhuXiaoBing-cn]

Current situation:
When I use aad b2c, I can get two types of issuer in the access token through user flow. They are:

• iss claims: https://xxxxb2c.b2clogin.com/<tenant-id>/v2.0/
• iss claims: https://xxxxb2c.b2clogin.com/tfp/<tenant-id>/<user-flow-name>/v2.0/

For the first type of issuer, the user flow name is not included, and there is no way to obtain OpenID Connect metadata documents through issuer splicing /.well-known/openid-configuration. The second issuer can do it.

Current thoughts:
A map, the key is used to store the trusted issuer, and value is used to store the well-known base uri. We need to process the well-known base uri for:

• The first type: when iss claims: https://xxxxb2c.b2clogin.com/<tenant-id>/v2.0/, we need to splice the well-knwon base uri into this https://xxxxb2c.b2clogin.com/43572109- xxxx-b9d264903c4e/<user-flow-name>/v2.0/.well-known/openid-configuration.

• The second type: when iss claims: https://xxxxb2c.b2clogin.com/tfp/43572109-xxxx-b9d264903c4e/<user-flow-name>/v2.0/, we need to splice the well-known base uri like this https://xxxxb2c.b2clogin.com/tfp/43572109-xxxx-b9d264903c4e/<user-flow-name>/v2.0/.well-known/openid-configuration.

Then, when requesting the aad b2c resource server, an access token received is analyzed to obtain an issuer claim. Compare it with the trusted Issuer, if the same, the well-known base uri will be obtained through the trusted Issuer.

Users only need to manually configure what they need.

[ZhuXiaoBing-cn]

Obtaining OpenID Provider Configuration Information: https://openid.net/specs/openid-connect-discovery-1_0.html#ProviderConfig