32.20. OAuth Support
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## 32.20. OAuth Support #

libpq implements support for the OAuth v2 Device Authorization client flow, documented in RFC 8628, as an optional module. See the installation documentation for information on how to enable support for Device Authorization as a builtin flow.

When support is enabled and the optional module installed, libpq will use the builtin flow by default if the server requests a bearer token during authentication. This flow can be utilized even if the system running the client application does not have a usable web browser, for example when running a client via SSH.

The builtin flow will, by default, print a URL to visit and a user code to enter there:

    $ psql 'dbname=postgres oauth_issuer=https://example.com oauth_client_id=...'
    Visit https://example.com/device and enter the code: ABCD-EFGH

(This prompt may be customized.) The user will then log into their OAuth provider, which will ask whether to allow libpq and the server to perform actions on their behalf. It is always a good idea to carefully review the URL and permissions displayed, to ensure they match expectations, before continuing. Permissions should not be given to untrusted third parties.

Client applications may implement their own flows to customize interaction and integration with applications. See Section 32.20.1 for more information on how add a custom flow to libpq.

For an OAuth client flow to be usable, the connection string must at minimum contain oauth_issuer and oauth_client_id. (These settings are determined by your organization's OAuth provider.) The builtin flow additionally requires the OAuth authorization server to publish a device authorization endpoint.

### Note

The builtin Device Authorization flow is not currently supported on Windows. Custom client flows may still be implemented.

### 32.20.1. Authdata Hooks #

The behavior of the OAuth flow may be modified or replaced by a client using the following hook API:

`PQsetAuthDataHook` #

  Sets the `PGauthDataHook`, overriding libpq's handling of one or more aspects of its OAuth client flow.

      void PQsetAuthDataHook(PQauthDataHook_type hook);

  If `hook` is `NULL`, the default handler will be reinstalled. Otherwise, the application passes a pointer to a callback function with the signature:

      int hook_fn(PGauthData type, PGconn *conn, void *data);

  which libpq will call when an action is required of the application. `type` describes the request being made, `conn` is the connection handle being authenticated, and `data` points to request-specific metadata. The contents of this pointer are determined by `type`; see Section 32.20.1.1 for the supported list.

  Hooks can be chained together to allow cooperative and/or fallback behavior. In general, a hook implementation should examine the incoming `type` (and, potentially, the request metadata and/or the settings for the particular `conn` in use) to decide whether or not to handle a specific piece of authdata. If not, it should delegate to the previous hook in the chain (retrievable via `PQgetAuthDataHook`).

  Success is indicated by returning an integer greater than zero. Returning a negative integer signals an error condition and abandons the connection attempt. (A zero value is reserved for the default implementation.)

`PQgetAuthDataHook` #

  Retrieves the current value of `PGauthDataHook`.

      PQauthDataHook_type PQgetAuthDataHook(void);

  At initialization time (before the first call to `PQsetAuthDataHook`), this function will return `PQdefaultAuthDataHook`.

#### 32.20.1.1. Hook Types #

The following `PGauthData` types and their corresponding `data` structures are defined:

`PQAUTHDATA_PROMPT_OAUTH_DEVICE` #

  Replaces the default user prompt during the builtin device authorization client flow. `data` points to an instance of `PGpromptOAuthDevice`:

      typedef struct _PGpromptOAuthDevice
      {
          const char *verification_uri;   /* verification URI to visit */
          const char *user_code;          /* user code to enter */
          const char *verification_uri_complete;  /* optional combination of URI and
                                                   * code, or NULL */
          int         expires_in;         /* seconds until user code expires */
      } PGpromptOAuthDevice;

  The OAuth Device Authorization flow which can be included in libpq requires the end user to visit a URL with a browser, then enter a code which permits libpq to connect to the server on their behalf. The default prompt simply prints the `verification_uri` and `user_code` on standard error. Replacement implementations may display this information using any preferred method, for example with a GUI.

  This callback is only invoked during the builtin device authorization flow. If the application installs a custom OAuth flow, or libpq was not built with support for the builtin flow, this authdata type will not be used.

  If a non-NULL `verification_uri_complete` is provided, it may optionally be used for non-textual verification (for example, by displaying a QR code). The URL and user code should still be displayed to the end user in this case, because the code will be manually confirmed by the provider, and the URL lets users continue even if they can't use the non-textual method. For more information, see section 3.3.1 in RFC 8628.

`PQAUTHDATA_OAUTH_BEARER_TOKEN` #

  Adds a custom implementation of a flow, replacing the builtin flow if it is installed. The hook should either directly return a Bearer token for the current user/issuer/scope combination, if one is available without blocking, or else set up an asynchronous callback to retrieve one.

  `data` points to an instance of `PGoauthBearerRequest`, which should be filled in by the implementation:

      typedef struct PGoauthBearerRequest
      {
          /* Hook inputs (constant across all calls) */
          const char *openid_configuration; /* OIDC discovery URL */
          const char *scope;                /* required scope(s), or NULL */

          /* Hook outputs */

          /*
           * Callback implementing a custom asynchronous OAuth flow. The signature is
           * platform-dependent: PQ_SOCKTYPE is SOCKET on Windows, and int everywhere
           * else.
           */
          PostgresPollingStatusType (*async) (PGconn *conn,
                                              struct PGoauthBearerRequest *request,
                                              PQ_SOCKTYPE *altsock);

          /* Callback to clean up custom allocations. */
          void        (*cleanup) (PGconn *conn, struct PGoauthBearerRequest *request);

          char       *token;   /* acquired Bearer token */
          void       *user;    /* hook-defined allocated data */
      } PGoauthBearerRequest;

  Two pieces of information are provided to the hook by libpq: `openid_configuration` contains the URL of an OAuth discovery document describing the authorization server's supported flows, and `scope` contains a (possibly empty) space-separated list of OAuth scopes which are required to access the server. Either or both may be `NULL` to indicate that the information was not discoverable. (In this case, implementations may be able to establish the requirements using some other preconfigured knowledge, or they may choose to fail.)

  The final output of the hook is `token`, which must point to a valid Bearer token for use on the connection. (This token should be issued by the oauth_issuer and hold the requested scopes, or the connection will be rejected by the server's validator module.) The allocated token string must remain valid until libpq is finished connecting; the hook should set a `cleanup` callback which will be called when libpq no longer requires it.

  If an implementation cannot immediately produce a `token` during the initial call to the hook, it should set the `async` callback to handle nonblocking communication with the authorization server. [16] This will be called to begin the flow immediately upon return from the hook. When the callback cannot make further progress without blocking, it should return either `PGRES_POLLING_READING` or `PGRES_POLLING_WRITING` after setting `*altsock` to the file descriptor that will be marked ready to read/write when progress can be made again. (This descriptor is then provided to the top-level polling loop via `PQsocket()`.) Return `PGRES_POLLING_OK` after setting `token` when the flow is complete, or `PGRES_POLLING_FAILED` to indicate failure.

  Implementations may wish to store additional data for bookkeeping across calls to the `async` and `cleanup` callbacks. The `user` pointer is provided for this purpose; libpq will not touch its contents and the application may use it at its convenience. (Remember to free any allocations during token cleanup.)

### 32.20.2. Debugging and Developer Settings #

A "dangerous debugging mode" may be enabled by setting the environment variable `PGOAUTHDEBUG=UNSAFE`. This functionality is provided for ease of local development and testing only. It does several things that you will not want a production system to do:

- permits the use of unencrypted HTTP during the OAuth provider exchange

- allows the system's trusted CA list to be completely replaced using the `PGOAUTHCAFILE` environment variable

- prints HTTP traffic (containing several critical secrets) to standard error during the OAuth flow

- permits the use of zero-second retry intervals, which can cause the client to busy-loop and pointlessly consume CPU

### Warning

Do not share the output of the OAuth flow traffic with third parties. It contains secrets that can be used to attack your clients and servers.

[16] Performing blocking operations during the `PQAUTHDATA_OAUTH_BEARER_TOKEN` hook callback will interfere with nonblocking connection APIs such as `PQconnectPoll` and prevent concurrent connections from making progress. Applications which only ever use the synchronous connection primitives, such as `PQconnectdb`, may synchronously retrieve a token during the hook instead of implementing the `async` callback, but they will necessarily be limited to one connection at a time.

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