A certificate used by an application deserves its own migration check. Copying documents does not establish that the new Mac can perform the authorised task associated with that certificate or key.

Ask the application owner or administrator which items and export format are required. Confirm that you are allowed to move them. Record non-secret identifiers such as the certificate name and intended service, while keeping private keys and export passwords out of screenshots and handover messages.

Export the intended items

Apple documents that Keychain Access can export some items, including certificates and keys. It cannot export saved passwords; those use the separate Passwords workflow.

Open Keychain Access through Spotlight and select the required items. Choose File, Export Items. If that command is dimmed, Apple says at least one selected item cannot be exported. Review the selection instead of assuming that every item in the keychain can be copied together.

Choose a protected destination and the format required by the receiving workflow, then save. Set the export password when prompted and retain it securely. Apple notes that some exported items, such as public keys, do not require a password; an absent password prompt does not prove that you exported the complete identity your application needs.

Check the receiving application

On the destination Mac, use File, Import Items in Keychain Access, select the exported file and choose the intended destination keychain. Complete its legitimate authentication prompts.

Inspect the imported item and then test the authorised application operation. Seeing a familiar certificate name in Keychain Access is only an intermediate check. The application may require a particular certificate-and-key arrangement or an administrator’s enrolment process.

Keep the source items until the destination has been accepted. Do not change certificate trust to Always Trust as a general migration fix. If the application rejects the imported material, preserve the exact error and confirm its requirements with the administrator.

Once the transfer is accepted, handle temporary export files according to the organisation’s credential-storage policy. They should not remain as unexplained attachments or files in a shared Downloads folder.

References: Apple: importing and exporting keychain items.