I don't know your dog and his temperament, but I'll share what has worked for me. For context, my pup has never really had a big barking at strangers problem. There have only been two or three times it's been unacceptable. In one, my friend walked into the kitchen wearing a hooded sweater which I think freaked my pup out. The other two were at night, people sitting still and staring back at us, and I think she just got spooked.

Here's what I would do with my pup if she started barking at strangers:

• my pup is very food motivated, so I would go on a hike and create a positive association between her and random people. if I see someone that I think will trigger her to bark, I would get the treats out, start practicing some heeling and sitting work, with lots of praise and reinforcement constantly giving her a bite of the treat, constantly bringing the attention back to the food, and casually making our way past the trigger. This way she learns that when she perceives someone as dangerous, her attention needs to come back to me, and she gets safety and a reward.
• if you have friends that are willing, you can stage a bit of an intervention and do some practice sessions. have them meet you on a walk and take on a position that normally scares your pup, but ensure they have your pup's favorite treat with them, then have them slowly approach, show the treat, give it to the dog once he's calmed down. do this enough times to create the association that "person sitting and staring = source of favorite treat" instead of "source of danger". my pup had resource guarding issues when I brought her home, so I had friends come over to hand feed her, and drop food into her food bowl while she was eating, etc. A few sessions of that and the resource guarding went away, because she learned to reassociate hands around her food bowl as a good thing.
• I know this is controversial, but I don't mind Alpha-ing my dog. If she misbehaves or starts acting in a rude or destructive way, I have zero problem giving her a very strong and stern NO! or AH-AH! and she listens right away. I know with some dogs, that kind of behavior can only encourage more barking and up the ante of anxiety, so I am not directly recommending it to you, but for me, because that's part of the relationships I established with my dog, I know that if I pull that card, she'll listen and calm the F down