How to get data from webservices and save that in S3

You can take a look at the documentation where it explains the process for uploading objects to s3 files via Amazon S3 console, AWS SDKs, REST API or CLI.

For adding objects to an S3 bucket the requesting entity would need permission to complete the PUT request. This can be accomplished by Identity and Access Management in the AWS account. There a policy can be attached to a User or Role giving that entity permission to complete the PUT request. Additionally, with S3 bucket policies you can further restrict access to the bucket for increased security: https://docs.aws.amazon.com/AmazonS3/latest/userguide/example-bucket-policies.html

If the web services you are referring to are located in a Virtual Private Cloud (VPC), a recommended method to put objects into S3 is via a S3 Gateway Endpoint. This connection will allow the object to be written directly to S3 from the VPC without traversing the internet. This type of gateway service is free.

https://docs.aws.amazon.com/vpc/latest/privatelink/vpc-endpoints-s3.html