Legal, Legitimate, Lawful

Lawful. In accordance with the law of the land; according to the law; permitted, sanctioned, or justified by law. “Lawful” properly implies a thing conformable to or enjoined by law; “Legal”, a thing in the form or after the manner of law or binding by law. A writ or warrant issuing from any court, under color of law, is a “legal” process however defective. See legal. [Bold emphasis added]

I agree with Doll, it seems a good answer to me. I would only add that the word "legitimate" refers to to "something emerged from law", created by the effect of legal provisions, approved and enforced by law - for example "legitimate right of the owner to dispose with his property".
Concerning "legal", in the way presented by Doll, it can be substituted by the word "juristic" - created

I slightly differ from the answers above. Legitimate in not enforceable by Law whereas "LEGAL" is enforceable. A small example. To cross a road at "Zebra Crossing" or "Cross Walk" is required by law so if you cross from any other point on walk on the road it is illegitimate or unlawful, because it is not provided in the trafic rule, so it is not illegal. The rule says one must cross the road at th