Validators call delegates before checking if validation should occur

[mafurman]

Fixes #1100.

Ex. TokenValidationParameters.AudienceValidator is called before the value of TokenValidationParameters.ValidateAudience is checked.

[henrik-me]

                        return;

for my education: Would there ever be a situation where there would be multiple audiences which could be valid? (the method takes an enum of audiences), can you pls. help describe the scenario in which this would happen?

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Refers to: src/Microsoft.IdentityModel.Tokens/Validators.cs:93 in dc9b6b5. [](commit_id = dc9b6b5, deletion_comment = False)

[mafurman]

                        return;

for my education: Would there ever be a situation where there would be multiple audiences which could be valid? (the method takes an enum of audiences), can you pls. help describe the scenario in which this would happen?

Refers to: src/Microsoft.IdentityModel.Tokens/Validators.cs:93 in dc9b6b5. [](commit_id = dc9b6b5, deletion_comment = False)

@henrik-me I believe this would mainly be used in the scenario where you could have multiple different represenations of the same audience.

[mafurman]

This PR has been rebased against dev (previously was dev5x).

[AndersAbel]

                        return;

for my education: Would there ever be a situation where there would be multiple audiences which could be valid? (the method takes an enum of audiences), can you pls. help describe the scenario in which this would happen?

Refers to: src/Microsoft.IdentityModel.Tokens/Validators.cs:93 in dc9b6b5. [](commit_id = dc9b6b5, deletion_comment = False)

Yes, it is sometimes used for multitenancy SAS deployments. When each tenant/customer has their own domain that is just a CNAME to a common hosting instance each tenant might have their own audience value. The validation on the common host would then accept an audience value for any of the tenant hosts.