feat(session): add create session cookie feature

* Add free standing function sessions::create_session_cookie(credentials, id_token, duration)
* Add example

Signed-off-by: Stephane Eintrazi <[email protected]>
Signed-off-by: David Graeff <[email protected]>

examples/readme.md

@@ -23,6 +23,17 @@ identified by the firebase user id.
 
 * Build and run with `cargo run --example firebase_user`.
 
+## Session cookie example
+
+This example shows how to exchange a ID token, usually given by the firebase web framework on the client side,
+into a server-side session cookie.
+
+Firebase Auth provides server-side session cookie management for traditional websites that rely on session cookies.
+This solution has several advantages over client-side short-lived ID tokens,
+which may require a redirect mechanism each time to update the session cookie on expiration.
+
+* Build and run with `cargo run --example session_cookie`.
+
 ## Rocket Protected Route example
 
 [Rocket](https://rocket.rs) is a an easy to use web-framework for Rust.

examples/session_cookie.rs

@@ -0,0 +1,41 @@
+use firestore_db_and_auth::{
+    errors::FirebaseError, Credentials, FirebaseAuthBearer, sessions::session_cookie
+};
+
+use chrono::Duration;
+
+mod utils;
+
+fn main() -> Result<(), FirebaseError> {
+    // Search for a credentials file in the root directory
+    use std::path::PathBuf;
+
+    let mut credential_file = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    credential_file.push("firebase-service-account.json");
+    let mut cred = Credentials::from_file(credential_file.to_str().unwrap())?;
+
+    // Only download the public keys once, and cache them.
+    let jwkset = utils::from_cache_file(credential_file.with_file_name("cached_jwks.jwks").as_path(), &cred)?;
+    cred.add_jwks_public_keys(&jwkset);
+    cred.verify()?;
+
+    let cookie = session_cookie::create(&cred, user_session.access_token(), Duration::seconds(3600))?;
+    println!("Created session cookie: {}", cookie);
+
+    Ok(())
+}
+
+#[test]
+fn create_session_cookie_test() -> Result<(), FirebaseError> {
+    let cred = utils::valid_test_credentials()?;
+    let user_session = utils::user_session_with_cached_refresh_token(&cred)?;
+
+    assert_eq!(user_session.user_id, utils::TEST_USER_ID);
+    assert_eq!(user_session.project_id(), cred.project_id);
+
+    use chrono::Duration;
+    let cookie = session_cookie::create(&cred, user_session.access_token(), Duration::seconds(3600))?;
+
+    assert!(cookie.len() > 0);
+    Ok(())
+}

src/jwt.rs

@@ -141,8 +141,8 @@ pub(crate) fn create_jwt<S>(
     user_id: Option<String>,
     audience: &str,
 ) -> Result<AuthClaimsJWT, Error>
-where
-    S: AsRef<str>,
+    where
+        S: AsRef<str>,
 {
     use std::ops::Add;
 
@@ -242,3 +242,57 @@ pub(crate) fn verify_access_token(
         audience,
     })
 }
+
+pub mod session_cookie {
+    use super::*;
+    use std::ops::Add;
+
+    pub(crate) fn create_jwt_encoded(
+        credentials: &Credentials,
+        duration: chrono::Duration,
+    ) -> Result<String, Error> {
+        let scope = [
+            "https://www.googleapis.com/auth/cloud-platform",
+            "https://www.googleapis.com/auth/firebase.database",
+            "https://www.googleapis.com/auth/firebase.messaging",
+            "https://www.googleapis.com/auth/identitytoolkit",
+            "https://www.googleapis.com/auth/userinfo.email",
+        ];
+
+        const AUDIENCE: &str = "https://accounts.google.com/o/oauth2/token";
+
+        use biscuit::{
+            jws::{Header, RegisteredHeader},
+            ClaimsSet, Empty, RegisteredClaims, JWT,
+        };
+
+        let header: Header<Empty> = Header::from(RegisteredHeader {
+            algorithm: SignatureAlgorithm::RS256,
+            key_id: Some(credentials.private_key_id.to_owned()),
+            ..Default::default()
+        });
+        let expected_claims = ClaimsSet::<JwtOAuthPrivateClaims> {
+            registered: RegisteredClaims {
+                issuer: Some(credentials.client_email.clone()),
+                audience: Some(SingleOrMultiple::Single(AUDIENCE.to_string())),
+                subject: Some(credentials.client_email.clone()),
+                expiry: Some(biscuit::Timestamp::from(Utc::now().add(duration))),
+                issued_at: Some(biscuit::Timestamp::from(Utc::now())),
+                ..Default::default()
+            },
+            private: JwtOAuthPrivateClaims {
+                scope: Some(scope.join(" ")),
+                client_id: None,
+                uid: None,
+            },
+        };
+        let jwt = JWT::new_decoded(header, expected_claims);
+
+        let secret = credentials
+            .keys
+            .secret
+            .as_ref()
+            .ok_or(Error::Generic("No private key added via add_keypair_key!"))?;
+        Ok(jwt.encode(&secret.deref())?.encoded()?.encode())
+    }
+}

src/sessions.rs

@@ -5,8 +5,8 @@
 use super::credentials;
 use super::errors::{extract_google_api_error, FirebaseError};
 use super::jwt::{
-    create_jwt, is_expired, jwt_update_expiry_if, verify_access_token, AuthClaimsJWT, JWT_AUDIENCE_FIRESTORE,
-    JWT_AUDIENCE_IDENTITY,
+    create_jwt, is_expired, jwt_update_expiry_if, verify_access_token, AuthClaimsJWT,
+    JWT_AUDIENCE_FIRESTORE, JWT_AUDIENCE_IDENTITY,
 };
 use super::FirebaseAuthBearer;
 
@@ -58,7 +58,7 @@ pub mod user {
         /// Returns the current access token.
         /// This method will automatically refresh your access token, if it has expired.
         ///
-        /// If the refresh failed, this will
+        /// If the refresh failed, this will return an empty string.
         fn access_token(&self) -> String {
             let jwt = self.access_token_.borrow();
             let jwt = jwt.as_str();
@@ -258,12 +258,23 @@ pub mod user {
             })
         }
 
-        pub fn by_access_token(credentials: &Credentials, firebase_tokenid: &str) -> Result<Session, FirebaseError> {
-            let result = verify_access_token(&credentials, firebase_tokenid)?;
+        /// Create a new firestore user session by a valid access token
+        ///
+        /// Remember that such a session cannot renew itself. As soon as the access token expired,
+        /// no further operations can be issued by this session.
+        ///
+        /// No network operation is performed, the access token is only checked for its validity.
+        ///
+        /// Arguments:
+        /// - `credentials` The credentials
+        /// - `access_token` An access token, sometimes called a firebase id token.
+        ///
+        pub fn by_access_token(credentials: &Credentials, access_token: &str) -> Result<Session, FirebaseError> {
+            let result = verify_access_token(&credentials, access_token)?;
             Ok(Session {
                 user_id: result.subject,
                 project_id_: result.audience,
-                access_token_: RefCell::new(firebase_tokenid.to_owned()),
+                access_token_: RefCell::new(access_token.to_owned()),
                 refresh_token: None,
                 api_key: credentials.api_key.clone(),
                 client: reqwest::blocking::Client::new(),
@@ -273,6 +284,92 @@ pub mod user {
     }
 }
 
+pub mod session_cookie {
+    use super::*;
+
+    pub static GOOGLE_OAUTH2_URL: &str = "https://accounts.google.com/o/oauth2/token";
+
+    /// See https://cloud.google.com/identity-platform/docs/reference/rest/v1/projects/createSessionCookie
+    #[inline]
+    fn identitytoolkit_url(project_id: &str) -> String {
+        format!("https://identitytoolkit.googleapis.com/v1/projects/{}:createSessionCookie", project_id)
+    }
+
+    /// See https://cloud.google.com/identity-platform/docs/reference/rest/v1/CreateSessionCookieResponse
+    #[derive(Debug, Deserialize)]
+    struct CreateSessionCookieResponseDTO {
+        #[serde(rename = "sessionCookie")]
+        session_cookie_jwk: String,
+    }
+
+    /// https://cloud.google.com/identity-platform/docs/reference/rest/v1/projects/createSessionCookie
+    #[derive(Debug, PartialEq, Eq, Deserialize, Serialize)]
+    struct SessionLoginDTO {
+        /// Required. A valid Identity Platform ID token.
+        #[serde(rename = "idToken")]
+        id_token: String,
+        /// The number of seconds until the session cookie expires. Specify a duration in seconds, between five minutes and fourteen days, inclusively.
+        #[serde(rename = "validDuration")]
+        valid_duration: u64,
+        #[serde(rename = "tenantId")]
+        #[serde(skip_serializing_if = "Option::is_none")]
+        tenant_id: Option<String>,
+    }
+
+    #[derive(Debug, Deserialize)]
+    struct Oauth2ResponseDTO {
+        access_token: String,
+        expires_in: u64,
+        token_type: String,
+    }
+
+    /// Firebase Auth provides server-side session cookie management for traditional websites that rely on session cookies.
+    /// This solution has several advantages over client-side short-lived ID tokens,
+    /// which may require a redirect mechanism each time to update the session cookie on expiration:
+    ///
+    /// * Improved security via JWT-based session tokens that can only be generated using authorized service accounts.
+    /// * Stateless session cookies that come with all the benefit of using JWTs for authentication.
+    ///   The session cookie has the same claims (including custom claims) as the ID token, making the same permissions checks enforceable on the session cookies.
+    /// * Ability to create session cookies with custom expiration times ranging from 5 minutes to 2 weeks.
+    /// * Flexibility to enforce cookie policies based on application requirements: domain, path, secure, httpOnly, etc.
+    /// * Ability to revoke session cookies when token theft is suspected using the existing refresh token revocation API.
+    /// * Ability to detect session revocation on major account changes.
+    ///
+    /// See https://firebase.google.com/docs/auth/admin/manage-cookies
+    ///
+    /// The generated session cookie is a JWT that includes the firebase user id in the "sub" (subject) field.
+    ///
+    /// Arguments:
+    /// - `credentials` The credentials
+    /// - `id_token` An access token, sometimes called a firebase id token.
+    /// - `duration` The cookie duration
+    ///
+    pub fn create(credentials: &credentials::Credentials, id_token: String, duration: chrono::Duration) -> Result<String, FirebaseError> {
+        // Generate the assertion from the admin credentials
+        let assertion = crate::jwt::session_cookie::create_jwt_encoded(credentials, duration)?;
+
+        // Request Google Oauth2 to retrieve the access token in order to create a session cookie
+        let client = reqwest::blocking::Client::new();
+        let response_oauth2: Oauth2ResponseDTO = client.post(GOOGLE_OAUTH2_URL)
+            .form(&[("grant_type", "urn:ietf:params:oauth:grant-type:jwt-bearer"), ("assertion", &assertion)])
+            .send()?
+            .json()?;
+
+        // Create a session cookie with the access token previously retrieved
+        let response_session_cookie_json: CreateSessionCookieResponseDTO = client.post(&identitytoolkit_url(&credentials.project_id))
+            .bearer_auth(&response_oauth2.access_token)
+            .json(&SessionLoginDTO {
+                id_token,
+                valid_duration: duration.num_seconds() as u64,
+                tenant_id: None,
+            })
+            .send()?
+            .json()?;
+
+        Ok(response_session_cookie_json.session_cookie_jwk)
+    }
+}
+
 /// Find the service account session defined in here
 pub mod service_account {
     use super::*;