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use hex::encode as encode_hex;
use hmac::{Hmac, Mac, NewMac};
use sha2::Sha256;
type HmacSha256 = Hmac<Sha256>;
use constant_time_eq::constant_time_eq;
use std::collections::HashMap;
use std::error::Error;
use std::fmt::{Debug, Display};
#[derive(Debug)]
struct InvalidKeyValuePair;
impl Display for InvalidKeyValuePair {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
write!(f, "invalid key value pair")
}
}
impl Error for InvalidKeyValuePair {}
pub(crate) fn compute_signature(payload: &str, secret: &str) -> String {
let mut mac = HmacSha256::new_varkey(secret.as_bytes()).expect("HMAC can take key of any size");
mac.update(payload.as_bytes());
let result = mac.finalize();
let result = result.into_bytes().as_slice().to_vec();
encode_hex(result)
}
pub(crate) fn parse_stripe_signature_header(
header: &str,
) -> Result<HashMap<String, String>, Box<dyn Error>> {
let signature = header.trim().to_string();
let signature: Vec<&str> = signature.split(",").collect();
let signature: Vec<Vec<&str>> = signature
.iter()
.map(|pair| pair.split("=").map(|s| s.trim()).collect())
.collect();
let mut values: HashMap<String, String> = HashMap::new();
for pair in &signature {
if pair.len() != 2 {
return Err(Box::new(InvalidKeyValuePair));
}
let key = pair.first();
let value = pair.last();
values.insert(key.unwrap().to_string(), value.unwrap().to_string());
}
Ok(values)
}
pub fn verify(secret: &str, header: &str, payload: &str) -> Result<bool, Box<dyn Error>> {
let parsed_header = parse_stripe_signature_header(header)?;
let received_timestamp = parsed_header.get("t").ok_or(InvalidKeyValuePair)?;
let received_signature = parsed_header.get("v1").ok_or(InvalidKeyValuePair)?;
let payload = format!("{}.{}", received_timestamp, payload);
let expected_signature = &compute_signature(&payload, &secret);
Ok(constant_time_eq(
expected_signature.as_bytes(),
received_signature.as_bytes(),
))
}
#[cfg(test)]
mod tests {
use std::time::{SystemTime, UNIX_EPOCH};
use crate::compute_signature;
use crate::parse_stripe_signature_header;
use crate::verify;
pub(crate) fn generate_test_header(payload: String) -> String {
let start = SystemTime::now();
let timestamp = start
.duration_since(UNIX_EPOCH)
.expect("time went backwards")
.as_secs()
.to_string();
let payload = format!("{}.{}", timestamp, payload);
let signature = compute_signature(&payload, "really secure secret");
let header = format!("t={},v1={},v0=", timestamp, signature);
return header;
}
#[test]
fn it_parses_stripe_signature_header() {
let stripe_signature_header = generate_test_header("sample payload".to_string());
dbg!(&stripe_signature_header);
let values = parse_stripe_signature_header(&stripe_signature_header).unwrap();
assert!(values.get("t").is_some());
assert!(values.get("v1").is_some());
assert!(verify(
"really secure secret",
&stripe_signature_header,
"sample payload",
)
.unwrap());
}
}