We can use ‘Regular Expression Extractor’ to capture any dynamic data from the request and then it can be sent to subsequent requests using ‘BeanShell PreProcessor’. This approach makes it very simple to test APIs in which we need to get authentication token from the server and then passing it on all other requests.

You need to move your login under a controller. You can use an “Only Once Controller”. Then after the controller you can add the HTTP Header Manager with the Authorization header as “Bearer ${BEARER}” and it will read your variable.

More Info: read here

http://blogs.quovantis.com/jmeter-authorization-with-dynamic-access-token/