lohr: validate webhook signature
Previously lohr was unusable in a production setting, anyone could forge a malicious webhook and either: - mirror a private repo of yours to another remote they own - wipe a repo of yours by forcing mirroring from an empty mirror This is no longer the case!
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10
Cargo.lock
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10
Cargo.lock
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@ -336,6 +336,12 @@ dependencies = [
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"libc",
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]
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[[package]]
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name = "hex"
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version = "0.4.3"
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source = "registry+https://github.com/rust-lang/crates.io-index"
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checksum = "7f24254aa9a54b5c858eaee2f5bccdb46aaf0e486a595ed5fd8f86ba55232a70"
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[[package]]
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name = "hkdf"
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version = "0.10.0"
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@ -494,11 +500,15 @@ name = "lohr"
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version = "0.2.1"
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dependencies = [
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"anyhow",
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"hex",
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"hmac",
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"log 0.4.14",
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"rocket",
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"rocket_contrib",
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"serde",
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"serde_json",
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"serde_yaml",
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"sha2",
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]
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[[package]]
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@ -12,8 +12,12 @@ repository = "https://github.com/alarsyo/lohr"
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[dependencies]
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anyhow = "1.0.40"
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hex = "0.4.3"
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hmac = "0.10.1"
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log = "0.4.14"
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rocket = "0.4.7"
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rocket_contrib = { version = "0.4.7", features = [ "json" ] }
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serde = { version = "1.0.125", features = [ "derive" ] }
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serde_json = "1.0.64"
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serde_yaml = "0.8.17"
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sha2 = "0.9.3"
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14
README.org
14
README.org
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@ -29,20 +29,28 @@ Setting up =lohr= should be quite simple:
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1. Create a =Rocket.toml= file and [[https://rocket.rs/v0.4/guide/configuration/][add your configuration]].
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2. Run =lohr=:
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2. Export a secret variable:
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#+begin_src sh
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$ export LOHR_SECRET=42 # please don't use this secret
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#+end_src
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3. Run =lohr=:
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#+begin_src sh
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$ cargo run # or `cargo run --release` for production usage
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#+end_src
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3. Configure your favorite git server to send a webhook to =lohr='s address on
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4. Configure your favorite git server to send a webhook to =lohr='s address on
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every push event.
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I used [[https://docs.gitea.io/en-us/webhooks/][Gitea's webhooks format]], but I *think* they're similar to GitHub and
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GitLab's webhooks, so these should work too! (If they don't, *please* file an
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issue!)
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4. Add a =.lohr= file containing the remotes you want to mirror this repo to:
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Don't forget to set the webhook secret to the one you chose above.
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5. Add a =.lohr= file containing the remotes you want to mirror this repo to:
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#+begin_example
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git@github.com:you/your_repo
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11
src/main.rs
11
src/main.rs
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@ -10,7 +10,6 @@ use std::sync::{
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use std::thread;
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use rocket::{http::Status, post, routes, State};
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use rocket_contrib::json::Json;
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use log::error;
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@ -23,10 +22,14 @@ use job::Job;
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mod settings;
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use settings::GlobalSettings;
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mod signature;
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use signature::SignedJson;
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struct JobSender(Mutex<Sender<Job>>);
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struct Secret(String);
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#[post("/", data = "<payload>")]
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fn gitea_webhook(payload: Json<GiteaWebHook>, sender: State<JobSender>) -> Status {
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fn gitea_webhook(payload: SignedJson<GiteaWebHook>, sender: State<JobSender>) -> Status {
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// TODO: validate Gitea signature
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{
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@ -66,6 +69,9 @@ fn main() -> anyhow::Result<()> {
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let homedir: PathBuf = homedir.into();
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let homedir = homedir.canonicalize().expect("LOHR_HOME isn't valid!");
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let secret = env::var("LOHR_SECRET")
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.expect("please provide a secret, otherwise anyone can send you a malicious webhook");
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let config = parse_config(homedir.clone())?;
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thread::spawn(move || {
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@ -75,6 +81,7 @@ fn main() -> anyhow::Result<()> {
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rocket::ignite()
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.mount("/", routes![gitea_webhook])
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.manage(JobSender(Mutex::new(sender)))
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.manage(Secret(secret))
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.launch();
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Ok(())
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122
src/signature.rs
Normal file
122
src/signature.rs
Normal file
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@ -0,0 +1,122 @@
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use std::{
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io::{Read, Write},
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ops::{Deref, DerefMut},
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};
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use rocket::{
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data::{FromData, Outcome},
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http::ContentType,
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State,
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};
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use rocket::{
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data::{Transform, Transformed},
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http::Status,
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};
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use rocket::{Data, Request};
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use anyhow::anyhow;
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use serde::Deserialize;
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use crate::Secret;
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const X_GITEA_SIGNATURE: &str = "X-Gitea-Signature";
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fn validate_signature(secret: &str, signature: &str, data: &str) -> bool {
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use hmac::{Hmac, Mac, NewMac};
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use sha2::Sha256;
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type HmacSha256 = Hmac<Sha256>;
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let mut mac = HmacSha256::new_varkey(secret.as_bytes()).expect("this should never fail");
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mac.update(data.as_bytes());
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match hex::decode(signature) {
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Ok(bytes) => mac.verify(&bytes).is_ok(),
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Err(_) => false,
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}
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}
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pub struct SignedJson<T>(pub T);
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impl<T> Deref for SignedJson<T> {
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type Target = T;
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fn deref(&self) -> &T {
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&self.0
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}
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}
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impl<T> DerefMut for SignedJson<T> {
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fn deref_mut(&mut self) -> &mut T {
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&mut self.0
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}
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}
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const LIMIT: u64 = 1 << 20;
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// This is a one to one implementation of request_contrib::Json's FromData, but with HMAC
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// validation.
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//
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// Tracking issue for chaining Data guards to avoid this:
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// https://github.com/SergioBenitez/Rocket/issues/775
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impl<'a, T> FromData<'a> for SignedJson<T>
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where
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T: Deserialize<'a>,
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{
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type Error = anyhow::Error;
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type Owned = String;
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type Borrowed = str;
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fn transform(
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request: &Request,
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data: Data,
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) -> rocket::data::Transform<Outcome<Self::Owned, Self::Error>> {
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let size_limit = request.limits().get("json").unwrap_or(LIMIT);
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let mut s = String::with_capacity(512);
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match data.open().take(size_limit).read_to_string(&mut s) {
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Ok(_) => Transform::Borrowed(Outcome::Success(s)),
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Err(e) => Transform::Borrowed(Outcome::Failure((
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Status::BadRequest,
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anyhow!("couldn't read json: {}", e),
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))),
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}
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}
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fn from_data(request: &Request, o: Transformed<'a, Self>) -> Outcome<Self, Self::Error> {
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let json_ct = ContentType::new("application", "json");
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if request.content_type() != Some(&json_ct) {
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return Outcome::Failure((Status::BadRequest, anyhow!("wrong content type")));
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}
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let signatures = request.headers().get(X_GITEA_SIGNATURE).collect::<Vec<_>>();
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if signatures.len() != 1 {
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return Outcome::Failure((
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Status::BadRequest,
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anyhow!("request header needs exactly one signature"),
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));
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}
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let signature = signatures[0];
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let content = o.borrowed()?;
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let secret = request.guard::<State<Secret>>().unwrap();
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if !validate_signature(&secret.0, &signature, content) {
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return Outcome::Failure((Status::BadRequest, anyhow!("couldn't verify signature")));
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}
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let content = match serde_json::from_str(content) {
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Ok(content) => content,
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Err(e) => {
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return Outcome::Failure((
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Status::BadRequest,
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anyhow!("couldn't parse json: {}", e),
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))
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}
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};
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Outcome::Success(SignedJson(content))
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}
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}
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