Create a terraform.tfvars file in your terraform directory
If you give the name as mentioned above, terraform by default recognize that as a local environment file and you do not version control it.
Edit the file add these two variables
aws_access_key = "XXXXXXXXXXX"
aws_secret_key = "XXXX+XXXX"
In this way, you do not have to specifically mention the credentials every time you want to run:
If you create a file with a different name, you can pass the file name while running terraform commands
The above concept is keeping in mind AWS is the default provider and the credentials associated is the default user.