Design Authentication Manager

class AuthenticationManager:
    def __init__(self, timeToLive):
        self.ttl = timeToLive
        self.tokens = {}

    def generate(self, tokenId, currentTime) -> None:
        expirationTime = currentTime + self.ttl
        self.tokens[tokenId] = expirationTime

    def renew(self, tokenId, currentTime) -> None:
        if tokenId in self.tokens and self.tokens[tokenId] > currentTime:
            self.tokens[tokenId] = currentTime + self.ttl

    def countUnexpiredTokens(self, currentTime) -> int:
        count = 0
        for expirationTime in self.tokens.values():
            if expirationTime > currentTime:
                count = count + 1
        return count