official candidate
A candidate who has been officially endorsed by a political party or organization, typically for an election.
He ran in the election as the official candidate of the Liberal Democratic Party.
To become an official candidate, you must pass the party's screening process.
候補者 is a general term for any candidate, while 公認候補者 specifically means an officially endorsed candidate.
Compound of 公認 (official recognition/endorsement) and 候補者 (candidate).