51cd1206_JSON_Web_Token__JWT___Claim_Syntax
[Claim Name] nbf [JSON Value Type] number [Claim Semantics] The nbf (not before) claim identifies the time before which the token MUST NOT be accepted for processing. The processing of the nbf claim requires that the current date/time MUST be after or equal to the not-before date/time listed in the nbf claim. Implementers MAY provide for some small leeway, usually no more than a few minutes, to account for clock skew. This claim is OPTIONAL. [Claim Syntax] 
IntDate
I n t D a t e
S t r i n g O r U R I
S t r i n g
JSON Web Token (JWT)
Claim Syntax