The claim type identifier (ID) determines the Common Name (cn) of the claim type object in Active Directory. Normally, Active Roles automatically generates an ID when creating a claim type. The automatically generated ID has the following format:
ad://ext/attributeName:uniqueHexidecimalNumber
In this format, attributeName stands for the LDAP display name of the source attribute of the claim type, while uniqueHexidecimalNumber is a random-generated string of hexadecimal characters that ensures the uniqueness of the claim type ID.
To enable authorization scenarios where claims are used across a forest trust, you need to create claim types in both the trusted forest and trusting forest with the same claim type ID. Domain controllers in a trusting forest receiving claims from a trusted forest cannot understand these claims unless:
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Each claim has a claim type object created in both forests.
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The claim type ID in the trusting forest is identical to the claim type ID in the trusted forest.
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A Claim Transformation Policy Object is applied to allow incoming claims across the forest trust.
Therefore, when you create a claim type object, you may need to specify the appropriate claim type ID by hand. The option Set ID to a semantically identical claim type in a trusted forest serves this purpose, allowing you to type in an ID instead of having it created automatically. If you choose to enter an ID by hand, ensure that your ID string specifies a unique ID and conforms to the following format:
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Starts with the ad://ext/ prefix.
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The prefix is followed by 1 to 32 characters.
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Does not contain space characters or these characters: \ * ? " < > |.
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If a slash mark (/) occurs after the ad://ext/ prefix, then the slash mark must be surrounded by a character on each side. The surrounding character must not be a colon (:) or slash mark.
A valid example of an ID string is ad://ext/BusinessImpact.
The option Set ID to a semantically identical claim type in a trusted forest is available only when you create a claim type object. The ID should not be changed on existing claim type objects. When you create a claim type object, it is advisable to let an ID be generated automatically unless a business need justifies otherwise, such as the use of claim transformation policies in a multi-forest environment. This ensures that the newly created claim type has a valid, unique ID.