Un fichier entre deux machines, avec un code.

$ s3nd init --provider r2 --bucket transfers
Wrote /home/you/transfers/s3nd.config.json

Put the three values in .env, and keep it out of git:
  R2_ACCOUNT_ID=…
  R2_ACCESS_KEY_ID=…
  R2_SECRET_ACCESS_KEY=…
The R2 API token needs Object Read & Write on this bucket, and nothing else.
Give the bucket a lifecycle rule that deletes objects under "transfers/" after a day or two.
Run `s3nd doctor` — it performs the operations s3nd needs and reports what happened.

$ s3nd doctor
Using /home/you/transfers/s3nd.config.json
✓ Configuration: bucket "transfers", region "auto"
✓ Credentials: resolved, key ends in 1a2b
✓ Bucket reachable: HeadBucket succeeded
✓ Write, read, delete: round-tripped a probe object
! Expiry cleanup: no enabled expiration rule
  → Add an S3 lifecycle rule that expires objects under this bucket after a day or
    two. Without it, expired transfers stay stored and billed.

1 check(s) failed.

{
  "envFile": ".env",
  "profiles": {
    "r2": {
      "bucket": "transfers",
      "region": "auto",
      "endpoint": "https://${R2_ACCOUNT_ID}.r2.cloudflarestorage.com",
      "expiresIn": "24h",
      "credentials": { "accessKeyId": "${R2_ACCESS_KEY_ID}", "secretAccessKey": "${R2_SECRET_ACCESS_KEY}" }
    },
    "local": { "bucket": "transfers", "endpoint": "http://localhost:9000" },
    "prod":  { "remote": "https://drop.example.com/api/transfers", "token": "${S3ND_TOKEN}" }
  }
}

$ s3nd -p local doctor          # against a MinIO container, offline
$ s3nd -p r2 put ./report.pdf
$ s3nd -p prod put ./report.pdf # through your server, with a token

$ s3nd config                   # which value won, and where it came from
file         /home/you/transfers/s3nd.config.json (profile "r2")
mode         straight to S3
bucket       transfers                                 $S3ND_BUCKET
endpoint     https://8c4….r2.cloudflarestorage.com     s3nd.config.json (r2)
credentials  …1a2b                                     s3nd.config.json (r2)
expires in   1 day                                     s3nd.config.json (r2)