Adds the tough-ssm crate

This crate is meant to implement the KeySource trait for keys
that live in AWS SSM.

Cargo.toml

@@ -2,5 +2,6 @@
 members = [
     "olpc-cjson",
     "tough",
+    "tough-ssm",
     "tuftool",
 ]

tough-ssm/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "tough-ssm"
+version = "0.1.0"
+authors = ["Zac Mrowicki <mrowicki@amazon.com>"]
+edition = "2018"
+
+[features]
+default = ["rusoto"]
+rusoto = ["rusoto-rustls"]
+rusoto-native-tls = ["rusoto_core/native-tls", "rusoto_credential", "rusoto_ssm/native-tls"]
+rusoto-rustls = ["rusoto_core/rustls", "rusoto_credential", "rusoto_ssm/rustls"]
+
+[dependencies]
+tough = { version = "0.5.0", path = "../tough", features = ["http"] }
+rusoto_core = { version = "0.43", optional = true, default-features = false }
+rusoto_credential = { version = "0.43", optional = true }
+rusoto_ssm = { version = "0.43", optional = true, default-features = false }
+serde = "1.0.105"
+serde_json = "1.0.50"
+snafu = { version = "0.6.6", features = ["backtraces-impl-backtrace-crate"] }
+tokio = "0.2.13"

tough-ssm/src/client.rs

@@ -0,0 +1,53 @@
+// Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+use crate::error::{self, Result};
+use rusoto_core::{HttpClient, Region};
+use rusoto_credential::ProfileProvider;
+use rusoto_ssm::SsmClient;
+use snafu::ResultExt;
+use std::env;
+use std::str::FromStr;
+
+/// Builds an SSM client for a given profile name.
+///
+/// This **cannot** be called concurrently as it modifies environment variables (due to Rusoto's
+/// inflexibility for determining the region given a profile name).
+
+// A better explanation: we want to know what region to make SSM calls in based on ~/.aws/config,
+// but `ProfileProvider::region` is an associated function, not a method; this means we can't tell
+// it what profile to select the region for.
+//
+// However, `region` calls `ProfileProvider::default_profile_name`, which uses the `AWS_PROFILE`
+// environment variable. So we set that :(
+//
+// This behavior should be better supported in `rusoto_credential`: this PR
+// implements it: https://github.com/rusoto/rusoto/pull/1741
+// TODO: Update rusoto once the above PR is merged and all our problems magically dissapear!
+pub(crate) fn build_client(profile: Option<&str>) -> Result<SsmClient> {
+    Ok(if let Some(profile) = profile {
+        let mut provider = ProfileProvider::new().context(error::RusotoCreds)?;
+        provider.set_profile(profile);
+
+        let profile_prev = env::var_os("AWS_PROFILE");
+        env::set_var("AWS_PROFILE", profile);
+        let region = ProfileProvider::region().context(error::RusotoCreds)?;
+        match profile_prev {
+            Some(v) => env::set_var("AWS_PROFILE", v),
+            None => env::remove_var("AWS_PROFILE"),
+        }
+
+        SsmClient::new_with(
+            HttpClient::new().context(error::RusotoTls)?,
+            provider,
+            match region {
+                Some(region) => {
+                    Region::from_str(&region).context(error::RusotoRegion { region })?
+                }
+                None => Region::default(),
+            },
+        )
+    } else {
+        SsmClient::new(Region::default())
+    })
+}

tough-ssm/src/error.rs

@@ -0,0 +1,79 @@
+// Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+use snafu::{Backtrace, Snafu};
+
+pub type Result<T> = std::result::Result<T, Error>;
+
+/// The error type for this library.
+#[derive(Debug, Snafu)]
+#[snafu(visibility = "pub(crate)")]
+pub enum Error {
+    #[snafu(display("Unable to parse keypair: {}", source))]
+    KeyPairParse {
+        source: tough::error::Error,
+        backtrace: Backtrace,
+    },
+
+    #[snafu(display("Error creating AWS credentials provider: {}", source))]
+    RusotoCreds {
+        source: rusoto_credential::CredentialsError,
+        backtrace: Backtrace,
+    },
+
+    #[snafu(display("Unknown AWS region \"{}\": {}", region, source))]
+    RusotoRegion {
+        region: String,
+        source: rusoto_core::region::ParseRegionError,
+        backtrace: Backtrace,
+    },
+
+    #[snafu(display("Error creating AWS request dispatcher: {}", source))]
+    RusotoTls {
+        source: rusoto_core::request::TlsError,
+        backtrace: Backtrace,
+    },
+
+    #[snafu(display("Unable to create tokio runtime: {}", source))]
+    RuntimeCreation {
+        source: std::io::Error,
+        backtrace: Backtrace,
+    },
+
+    #[snafu(display(
+        "Failed to get aws-ssm://{}{}: {}",
+        profile.as_deref().unwrap_or(""),
+        parameter_name,
+        source,
+    ))]
+    SsmGetParameter {
+        profile: Option<String>,
+        parameter_name: String,
+        source: rusoto_core::RusotoError<rusoto_ssm::GetParameterError>,
+        backtrace: Backtrace,
+    },
+
+    #[snafu(display(
+        "Missing field in SSM response for parameter '{}': {}",
+        parameter_name,
+        field
+    ))]
+    SsmMissingField {
+        parameter_name: String,
+        field: &'static str,
+        backtrace: Backtrace,
+    },
+
+    #[snafu(display(
+        "Failed to put aws-ssm://{}{}: {}",
+        profile.as_deref().unwrap_or(""),
+        parameter_name,
+        source,
+    ))]
+    SsmPutParameter {
+        profile: Option<String>,
+        parameter_name: String,
+        source: rusoto_core::RusotoError<rusoto_ssm::PutParameterError>,
+        backtrace: Backtrace,
+    },
+}

tough-ssm/src/lib.rs

@@ -0,0 +1,79 @@
+// Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+mod client;
+pub mod error;
+
+use rusoto_ssm::Ssm;
+use snafu::{OptionExt, ResultExt};
+use tough::key_source::KeySource;
+use tough::sign::{parse_keypair, Sign};
+
+/// Implements the KeySource trait for keys that live in AWS SSM.
+#[derive(Debug)]
+pub struct SsmKeySource {
+    pub profile: Option<String>,
+    pub parameter_name: String,
+    pub key_id: Option<String>,
+}
+
+/// Implements the KeySource trait.
+impl KeySource for SsmKeySource {
+    fn as_sign(
+        &self,
+    ) -> std::result::Result<Box<dyn Sign>, Box<dyn std::error::Error + Send + Sync + 'static>>
+    {
+        let ssm_client = client::build_client(self.profile.as_deref())?;
+        let fut = ssm_client.get_parameter(rusoto_ssm::GetParameterRequest {
+            name: self.parameter_name.to_owned(),
+            with_decryption: Some(true),
+        });
+        let response = tokio::runtime::Runtime::new()
+            .context(error::RuntimeCreation)?
+            .block_on(fut)
+            .context(error::SsmGetParameter {
+                profile: self.profile.clone(),
+                parameter_name: &self.parameter_name,
+            })?;
+        let data = response
+            .parameter
+            .context(error::SsmMissingField {
+                parameter_name: &self.parameter_name,
+                field: "parameter",
+            })?
+            .value
+            .context(error::SsmMissingField {
+                parameter_name: &self.parameter_name,
+                field: "parameter.value",
+            })?
+            .as_bytes()
+            .to_vec();
+        let sign = Box::new(parse_keypair(&data).context(error::KeyPairParse)?);
+        Ok(sign)
+    }
+
+    fn write(
+        &self,
+        value: &str,
+        key_id_hex: &str,
+    ) -> std::result::Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
+        let ssm_client = client::build_client(self.profile.as_deref())?;
+        let fut = ssm_client.put_parameter(rusoto_ssm::PutParameterRequest {
+            name: self.parameter_name.to_owned(),
+            description: Some(key_id_hex.to_owned()),
+            key_id: self.key_id.as_ref().cloned(),
+            overwrite: Some(true),
+            type_: "SecureString".to_owned(),
+            value: value.to_owned(),
+            ..rusoto_ssm::PutParameterRequest::default()
+        });
+        tokio::runtime::Runtime::new()
+            .unwrap()
+            .block_on(fut)
+            .context(error::SsmPutParameter {
+                profile: self.profile.clone(),
+                parameter_name: &self.parameter_name,
+            })?;
+        Ok(())
+    }
+}