You can create a read-only deploy key.
Create a deploy key
   Arguments
  key    owner         owner [scalar] 
  The account owner of the repository. The name is not case sensitive.
       API:
Github Open API
(version: 1.1.4)
            key    repo         repo [scalar] 
  The name of the repository. The name is not case sensitive.
       API:
Github Open API
(version: 1.1.4)
             Returns
   201 application/json    deploy-key       deploy-key [object] 
  An SSH key granting access to a single repository.
       API:
Github Open API
(version: 1.1.4)
        422     validation_failed       validation_failed [scalar] 
  Validation failed, or the endpoint has been spammed.
       API:
Github Open API
(version: 1.1.4)
        API:
Github Open API
(version: 1.1.4)