Place 1 cup of the chicken broth into the slow cooker. Add the chicken breasts, drained diced tomatoes, taco seasoning, cayenne (if using), cream cheese pieces, and shredded Mexican blend cheese.
Cook on high for 1–2 hours (or on low 2–3 hours) until the chicken is cooked through and the cheeses have melted, stirring occasionally.
Remove the chicken breasts from the crockpot and shred them with two forks or a hand mixer; set aside.
In a small jar or bowl, whisk the remaining 1/2 cup chicken broth with the cornstarch until smooth, then pour the mixture into the crockpot and stir to combine with the cheese base.
Return the shredded chicken to the crockpot and add the rinsed, drained white beans. Stir until everything is evenly combined and heated through.
Taste and season with salt, black pepper, extra cayenne, or more taco seasoning if desired.
Garnish the dip with diced roma tomatoes, chopped cilantro, and sliced jalapeño peppers. Serve warm with tortilla chips, pita, or vegetables.