How could a person in the provinces be granted roman citizenship

There were no particular requirements for Roman citizenship just as there are no particular requirements for, say, British or American citizenship. (modern historical/constitutional testing excluded) The Romans were automatic citizens if their parents were citizens or if their parents were freed slaves. Some people of certain towns were granted blanket citizenship and some individuals were granted citizenship for service of some type to Rome, such as an auxiliary, being granted citizenship upon his completion of his service in the army.