You can do this using the following CLI commands:

Register a user

aws cognito-idp sign-up --region {your-aws-region} --client-id {your-client-id} --username admin@example.com --password password123

Confirm user registration

aws cognito-idp admin-confirm-sign-up --region {your-aws-region} --user-pool-id {your-user-pool-id} --username admin@example.com

Authenticate (get tokens)

aws cognito-idp admin-initiate-auth --region {your-aws-region} --cli-input-json file://auth.json

Where auth.json is:

{
    "UserPoolId": "{your-user-pool-id}",
    "ClientId": "{your-client-id}",
    "AuthFlow": "ADMIN_NO_SRP_AUTH",
    "AuthParameters": {
        "USERNAME": "admin@example.com",
        "PASSWORD": "password123"
    }
}

You should get a response like this if everything is set up correctly:

{
    "AuthenticationResult": {
        "ExpiresIn": 3600,
        "IdToken": "{your-idtoken}",
        "RefreshToken": "{your-refresh-token}",
        "TokenType": "Bearer",
        "AccessToken": "{your-access-token}"
    },
    "ChallengeParameters": {}
}

Use the following command to generate the auth tokens, fill in the xxxx appropriately based on your cognito configuration,

aws cognito-idp initiate-auth --auth-flow USER_PASSWORD_AUTH --client-id xxxx --auth-parameters USERNAME=xx@xx.com,PASSWORD=xxxx

Note: You can use any one username or password under applicable cognito user pool. The client can be found under general settings--> app client

The AccessKeyId and SecretAccessKey is not required as it already defined while setting up the aws cli. If not done use the following link to set that up first https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-configure.html

There is an AWS CLI command to generate Auth Tokens. You can use InitiateAuth CLI Command for this.

Note: Make sure you have done the UserPool configuration matching the expected tokens.