You can pull one or more secrets into the trigger by defining the name of the Kubernetes Secret and the key to use.

secretTargetRef:                          # Optional.
  - parameter: connectionString           # Required - Defined by the scale trigger
    name: my-keda-secret-entity           # Required.
    key: azure-storage-connectionstring   # Required.

Assumptions: namespace is in the same resource as referenced by in the ScaledObject, unless specified otherwise.