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If I have a generated Presigned URL that expired, should I be doing get_headers() (in PHP) to see if a 403 Forbidden error is thrown, otherwise use that same URL? Or is that a bad idea because it's an unnecessary GET request? Should I always just regenerate a new Presigned URL every time? I'm a little confused because there doesn't seem to be much information about this.
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In the Amazon S3 console, the maximum expiration time for a presigned URL is 12 hours from the time of creation.
Pre-signed URLs are used to provide short-term access to a private object in your S3 bucket. They work by appending an AWS Access Key, expiration time, and Sigv4 signature as query parameters to the S3 object. There are two common use cases when you may want to use them: Simple, occasional sharing of private files.
All objects and buckets are private by default. However, you can use a presigned URL to optionally share objects or allow your customers/users to upload objects to buckets without AWS security credentials or permissions.
There is an access check on the S3 side but that only checks whether the signer entity is allowed to get the file. You can remove that permission but that invalidates all signed URLs. Signed URLs provide secure a way to distribute private content without streaming them through the backend.
On macOS, use date -r 1535416265.
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The URL has the time it expires at.
Signature Version 2
htt ps://bucket.s3.amazonaws.com/foo.txt?AWSAccessKeyId=AKIAABCDEFGHIJK&Expires=1508608760&Signature=xxxxxxxxxxx
Expires gives the time in Unix timestamp (in seconds) and Coordinated Universal Time (UTC) .
$ date -d @1508608760
Sat Oct 21 17:59:20 UTC 2017
You can extract the value and compare it with the current time in UTC [time()], then decide to regenerate or not.
htt ps://s3.amazonaws.com/bucket/foo.txt?X-Amz-Algorithm=AWS4-HMAC-SHA256& X-Amz-Expires=3600&X-Amz-Credential=AKIAJRZXXXXXXXXus-east-1%2Fs3%2Faws4_request&X-Amz-SignedHeaders=host&X-Amz-Date=20171021T190750Z&X-Amz-Signature=8b84ae9b59e9f8a8d7066ecc39e797c8dc29848abcdef61717
X-Amz-Date gives the UTC time in ISO 8601 format.
You can extract the value, convert it to epoch/UTC and compare it with the current time in UTC [time()], then decide to regenerate or not.
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