To remediate the misconfiguration of database SSL certificate rotation for GCP using GCP CLI, follow these steps:

1. Open the Cloud Shell in the GCP Console.

2. Run the following command to list all the available instances:

gcloud sql instances list

3. Select the instance for which you want to rotate the SSL certificate and run the following command:

gcloud sql instances patch [INSTANCE_NAME] --database-flags ssl-cert-validity-period=90

4. Replace [INSTANCE_NAME] with the name of your instance.

5. This command sets the validity period of the SSL certificate to 90 days. You can change the value as per your requirement.

6. Once the command is executed successfully, the SSL certificate for the selected instance will be rotated every 90 days.

Note: Make sure that you have the necessary permissions to execute the above commands. Also, ensure that you have installed and configured the GCP CLI on your system.

To remediate the misconfiguration of rotating the database SSL certificate after every 90 days in GCP using Python, follow the steps below:

1. First, you need to create a Cloud Function in GCP to rotate the SSL certificate. To create a Cloud Function, follow the instructions given in the official documentation.

2. After creating the Cloud Function, you need to write a Python script that will rotate the SSL certificate. Here is an example script:

import google.auth
from google.cloud import spanner_v1
from datetime import datetime, timedelta

def rotate_ssl_certificate(request):
    # Authenticate with GCP
    credentials, project_id = google.auth.default()
    
    # Set the instance ID and database ID
    instance_id = 'your-instance-id'
    database_id = 'your-database-id'
    
    # Create a Spanner client
    spanner_client = spanner_v1.Client(project=project_id, credentials=credentials)
    
    # Get the instance and database objects
    instance = spanner_client.instance(instance_id)
    database = instance.database(database_id)
    
    # Get the current SSL certificate expiration date
    current_cert = database.get_iam_policy().bindings[0].condition.time
        
    # Calculate the new expiration date (90 days from now)
    new_cert = datetime.now() + timedelta(days=90)
    
    # Update the SSL certificate
    database.update_ddl([f"ALTER DATABASE `{database_id}` SET OPTIONS (ssl_cert_expiration='{new_cert.isoformat()}')"])
    
    # Return a success message
    return f"SSL certificate updated. New expiration date: {new_cert.isoformat()}"

3. In the above script, replace your-instance-id and your-database-id with the actual IDs of your Spanner instance and database.

4. Deploy the Cloud Function by clicking on the “Deploy” button in the Cloud Function console.

5. Finally, you need to schedule the Cloud Function to run every 90 days. To do this, go to the Cloud Scheduler console and create a new job. Set the frequency to “every 90 days” and the target to the Cloud Function you just created.

After completing these steps, your SSL certificate will be rotated every 90 days automatically.