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Based on the provided knowledge sources, Ory Hydra does not offer a separate API to directly obtain a login challenge. The login challenge is generated as part of the OAuth2/OpenID Connect flow when the end user's browser is redirected to the

/oauth2/auth

endpoint. This endpoint appends the

login_challenge

as a query parameter when redirecting to your login provider. To interact with the login challenge, you use the

/admin/oauth2/auth/requests/login

API to fetch information about an existing login request, but this requires that you already have the

login_challenge

value, which is initially provided via the

/oauth2/auth

browser flow [User login and consent flow](https://www.ory.sh/docs/oauth2-oidc/custom-login-consent/flow) [Hydra API Reference - getOAuth2LoginRequest](https://raw.githubusercontent.com/ory/hydra/master/spec/api.json). In summary: There is no API to generate or obtain a login challenge except through the

/oauth2/auth

endpoint, which is intended for browser-based flows. All other APIs (such as

/admin/oauth2/auth/requests/login

) require an existing

login_challenge

as input.

The knowledge sources do not provide a complete, explicit list of all possible query parameters for the Hydra

/oauth2/sessions/logout

API. However, based on the available documentation, the following parameters are mentioned as commonly used in the logout flow: - `id_token_hint`: The ID Token previously issued to the user. Including this helps identify the user session to be logged out, even if no session cookie exists. - `post_logout_redirect_uri`: The URI to which the user will be redirected after logout, if it is whitelisted for the client. - `state`: A value used to maintain state between the logout request and the response. These parameters are referenced in the context of OpenID Connect logout flows and are used to control the behavior of the logout process, including redirection and session identification [OpenID Connect logout](https://www.ory.sh/docs/oauth2-oidc/oidc-logout#redirect-after-logout) [OAuth2 logout not working](https://www.ory.sh/docs/hydra/debug/logout). Note: The knowledge sources do not provide a formal, exhaustive parameter table for this endpoint, so if you need a definitive list, please refer to the official Ory Hydra OpenAPI specification or the [Hydra API Reference](https://raw.githubusercontent.com/ory/hydra/master/spec/api.json).