Allow for PKCE flow without client secret + add docs (#25033)
The PKCE flow according to [RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636) allows for secure authorization without the requirement to provide a client secret for the OAuth app. It is implemented in Gitea since #5378 (v1.8.0), however without being able to omit client secret. Since #21316 Gitea supports setting client type at OAuth app registration. As public clients are already forced to use PKCE since #21316, in this PR the client secret check is being skipped if a public client is detected. As Gitea seems to implement PKCE authorization correctly according to the spec, this would allow for PKCE flow without providing a client secret. Also add some docs for it, please check language as I'm not a native English speaker. Closes #17107 Closes #25047
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Denys Konovalov
GitHub
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---
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date: "2019-04-19:44:00+01:00"
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date: "2023-06-01T08:40:00+08:00"
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title: "OAuth2 provider"
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slug: "oauth2-provider"
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weight: 41
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@ -40,7 +40,7 @@ At the moment Gitea only supports the [**Authorization Code Grant**](https://too
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- [Proof Key for Code Exchange (PKCE)](https://tools.ietf.org/html/rfc7636)
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- [OpenID Connect (OIDC)](https://openid.net/specs/openid-connect-core-1_0.html#CodeFlowAuth)
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To use the Authorization Code Grant as a third party application it is required to register a new application via the "Settings" (`/user/settings/applications`) section of the settings.
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To use the Authorization Code Grant as a third party application it is required to register a new application via the "Settings" (`/user/settings/applications`) section of the settings. To test or debug you can use the web-tool https://oauthdebugger.com/.
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## Scopes
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@ -87,17 +87,19 @@ Gitea supports both confidential and public client types, [as defined by RFC 674
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For public clients, a redirect URI of a loopback IP address such as `http://127.0.0.1/` allows any port. Avoid using `localhost`, [as recommended by RFC 8252](https://datatracker.ietf.org/doc/html/rfc8252#section-8.3).
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## Example
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## Examples
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### Confidential client
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**Note:** This example does not use PKCE.
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1. Redirect to user to the authorization endpoint in order to get their consent for accessing the resources:
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1. Redirect the user to the authorization endpoint in order to get their consent for accessing the resources:
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```curl
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https://[YOUR-GITEA-URL]/login/oauth/authorize?client_id=CLIENT_ID&redirect_uri=REDIRECT_URI&response_type=code&state=STATE
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```
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The `CLIENT_ID` can be obtained by registering an application in the settings. The `STATE` is a random string that will be send back to your application after the user authorizes. The `state` parameter is optional but should be used to prevent CSRF attacks.
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The `CLIENT_ID` can be obtained by registering an application in the settings. The `STATE` is a random string that will be sent back to your application after the user authorizes. The `state` parameter is optional, but should be used to prevent CSRF attacks.
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@ -107,7 +109,7 @@ For public clients, a redirect URI of a loopback IP address such as `http://127.
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https://[REDIRECT_URI]?code=RETURNED_CODE&state=STATE
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```
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2. Using the provided `code` from the redirect, you can request a new application and refresh token. The access token endpoints accepts POST requests with `application/json` and `application/x-www-form-urlencoded` body, for example:
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2. Using the provided `code` from the redirect, you can request a new application and refresh token. The access token endpoint accepts POST requests with `application/json` and `application/x-www-form-urlencoded` body, for example:
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```curl
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POST https://[YOUR-GITEA-URL]/login/oauth/access_token
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@ -134,7 +136,69 @@ For public clients, a redirect URI of a loopback IP address such as `http://127.
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}
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```
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The `CLIENT_SECRET` is the unique secret code generated for this application. Please note that the secret will only be visible after you created/registered the application with Gitea and cannot be recovered. If you lose the secret you must regenerate the secret via the application's settings.
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The `CLIENT_SECRET` is the unique secret code generated for this application. Please note that the secret will only be visible after you created/registered the application with Gitea and cannot be recovered. If you lose the secret, you must regenerate the secret via the application's settings.
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The `REDIRECT_URI` in the `access_token` request must match the `REDIRECT_URI` in the `authorize` request.
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3. Use the `access_token` to make [API requests](https://docs.gitea.io/en-us/api-usage#oauth2) to access the user's resources.
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### Public client (PKCE)
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PKCE (Proof Key for Code Exchange) is an extension to the OAuth flow which allows for a secure credential exchange without the requirement to provide a client secret.
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**Note**: Please ensure you have registered your OAuth application as a public client.
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To achieve this, you have to provide a `code_verifier` for every authorization request. A `code_verifier` has to be a random string with a minimum length of 43 characters and a maximum length of 128 characters. It can contain alphanumeric characters as well as the characters `-`, `.`, `_` and `~`.
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Using this `code_verifier` string, a new one called `code_challenge` is created by using one of two methods:
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- If you have the required functionality on your client, set `code_challenge` to be a URL-safe base64-encoded string of the SHA256 hash of `code_verifier`. In that case, your `code_challenge_method` becomes `S256`.
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- If you are unable to do so, you can provide your `code_verifier` as a plain string to `code_challenge`. Then you have to set your `code_challenge_method` as `plain`.
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After you have generated this values, you can continue with your request.
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1. Redirect the user to the authorization endpoint in order to get their consent for accessing the resources:
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```curl
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https://[YOUR-GITEA-URL]/login/oauth/authorize?client_id=CLIENT_ID&redirect_uri=REDIRECT_URI&response_type=code&code_challenge_method=CODE_CHALLENGE_METHOD&code_challenge=CODE_CHALLENGE&state=STATE
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```
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The `CLIENT_ID` can be obtained by registering an application in the settings. The `STATE` is a random string that will be sent back to your application after the user authorizes. The `state` parameter is optional, but should be used to prevent CSRF attacks.
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The user will now be asked to authorize your application. If they authorize it, the user will be redirected to the `REDIRECT_URL`, for example:
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```curl
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https://[REDIRECT_URI]?code=RETURNED_CODE&state=STATE
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```
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2. Using the provided `code` from the redirect, you can request a new application and refresh token. The access token endpoint accepts POST requests with `application/json` and `application/x-www-form-urlencoded` body, for example:
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```curl
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POST https://[YOUR-GITEA-URL]/login/oauth/access_token
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```
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```json
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{
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"client_id": "YOUR_CLIENT_ID",
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"code": "RETURNED_CODE",
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"grant_type": "authorization_code",
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"redirect_uri": "REDIRECT_URI",
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"code_verifier": "CODE_VERIFIER",
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}
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```
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Response:
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```json
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{
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"access_token": "eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXVCJ9.eyJnbnQiOjIsInR0IjowLCJleHAiOjE1NTUxNzk5MTIsImlhdCI6MTU1NTE3NjMxMn0.0-iFsAwBtxuckA0sNZ6QpBQmywVPz129u75vOM7wPJecw5wqGyBkmstfJHAjEOqrAf_V5Z-1QYeCh_Cz4RiKug",
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"token_type": "bearer",
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"expires_in": 3600,
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"refresh_token": "eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXVCJ9.eyJnbnQiOjIsInR0IjoxLCJjbnQiOjEsImV4cCI6MTU1NzgwNDMxMiwiaWF0IjoxNTU1MTc2MzEyfQ.S_HZQBy4q9r5SEzNGNIoFClT43HPNDbUdHH-GYNYYdkRfft6XptJBkUQscZsGxOW975Yk6RbgtGvq1nkEcklOw"
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}
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```
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The `REDIRECT_URI` in the `access_token` request must match the `REDIRECT_URI` in the `authorize` request.
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@ -695,7 +695,7 @@ func handleRefreshToken(ctx *context.Context, form forms.AccessTokenForm, server
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}
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// "The authorization server MUST ... require client authentication for confidential clients"
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// https://datatracker.ietf.org/doc/html/rfc6749#section-6
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if !app.ValidateClientSecret([]byte(form.ClientSecret)) {
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if app.ConfidentialClient && !app.ValidateClientSecret([]byte(form.ClientSecret)) {
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errorDescription := "invalid client secret"
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if form.ClientSecret == "" {
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errorDescription = "invalid empty client secret"
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@ -753,7 +753,7 @@ func handleAuthorizationCode(ctx *context.Context, form forms.AccessTokenForm, s
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})
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return
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}
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if !app.ValidateClientSecret([]byte(form.ClientSecret)) {
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if app.ConfidentialClient && !app.ValidateClientSecret([]byte(form.ClientSecret)) {
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errorDescription := "invalid client secret"
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if form.ClientSecret == "" {
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errorDescription = "invalid empty client secret"
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@ -120,6 +120,29 @@ func TestAccessTokenExchange(t *testing.T) {
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assert.True(t, len(parsed.RefreshToken) > 10)
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}
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func TestAccessTokenExchangeWithPublicClient(t *testing.T) {
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defer tests.PrepareTestEnv(t)()
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req := NewRequestWithValues(t, "POST", "/login/oauth/access_token", map[string]string{
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"grant_type": "authorization_code",
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"client_id": "ce5a1322-42a7-11ed-b878-0242ac120002",
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"redirect_uri": "http://127.0.0.1",
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"code": "authcodepublic",
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"code_verifier": "N1Zo9-8Rfwhkt68r1r29ty8YwIraXR8eh_1Qwxg7yQXsonBt",
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})
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resp := MakeRequest(t, req, http.StatusOK)
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type response struct {
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AccessToken string `json:"access_token"`
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TokenType string `json:"token_type"`
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ExpiresIn int64 `json:"expires_in"`
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RefreshToken string `json:"refresh_token"`
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}
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parsed := new(response)
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assert.NoError(t, json.Unmarshal(resp.Body.Bytes(), parsed))
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assert.True(t, len(parsed.AccessToken) > 10)
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assert.True(t, len(parsed.RefreshToken) > 10)
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}
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func TestAccessTokenExchangeJSON(t *testing.T) {
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defer tests.PrepareTestEnv(t)()
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req := NewRequestWithJSON(t, "POST", "/login/oauth/access_token", map[string]string{
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