Get a single CrossRealmTrust object identified by source and target realms or projects. An entity can get the CrossRealmTrust created for its realm or granted from its realm to other realms based on the "rlm" claim in the access token.

Access Control:

• The calling principal must have "readCrossRealmTrust" action permission for the resource "{realm}" in the "authorization" service. The "{realm}" here represents the HRN of the target realm.
• This permission is granted to all entities by default policy. This permission is also explicitly granted to all entities with roles OrgAdmin or CrossRealmTrustManager.
• The calling principal MUST NOT include a project scope.