Direct octave in Bach? (Fugue BWV 846)

I'm new to counterpoint, but AFAIK this type of motion — two voices moving in direct motion to a perfect consonance — is "forbidden" in counterpoint. I'm very curious as to how Bach (and other people more knowledgeable than me) might have justified this!

I'm new to counterpoint, but AFAIK this type of motion — two voices moving in direct motion to a perfect consonance — is "forbidden" in counterpoint. I'm very curious as to how Bach (and other people more knowledgeable than me) might have justified this!