In your sentence, the correct form is "has been," because your main verb ("is") is in the present tense. If the sentence were in past tense, you would say "had been": "John WAS soaking wet because he HAD been walking in the rain." "John IS soaking wet because he HAS been walking in the rain."

Yes both can be used, it depends if you are refering to the incident in the present or in the past, I think 'was' can also be used: ...he was walking in the rain. Have a great day.:)

Gray's explanation is clear and correct.

Has been is correct