keycloak-scim/authorization_services/topics/service-authorization-obtaining-permission-authentication.adoc

[[_authentication_methods]]
= Client Authentication Methods

Clients need to authenticate to the token endpoint in order to obtain an RPT. When using the `urn:ietf:params:oauth:grant-type:uma-ticket`
grant type, clients can use any of these authentication methods:

* *Bearer Token*
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Clients should send an access token as a Bearer credential in an HTTP Authorization header to the token endpoint.
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.Example: an authorization request using an access token to authenticate to the token endpoint
```bash
curl -X POST \
  http://${host}:${port}/auth/realms/${realm}/protocol/openid-connect/token \
  -H "Authorization: Bearer ${access_token}" \
  --data "grant_type=urn:ietf:params:oauth:grant-type:uma-ticket"
```
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This method is especially useful when the client is acting on behalf of a user.
In this case, the bearer token is an access token previously issued by {project_name} to some client acting on behalf
of a user (or on behalf of itself). Permissions will be evaluated considering the access context represented by the access token.
For instance, if the access token was issued to Client A acting on behalf of User A, permissions will be granted depending on
the resources and scopes to which User A has access.

* *Client Credentials*
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Clients can use any of the client authentication methods supported by {project_name}. For instance, client_id/client_secret or JWT.
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.Example: an authorization request using client id and client secret to authenticate to the token endpoint
```bash
curl -X POST \
  http://${host}:${port}/auth/realms/${realm}/protocol/openid-connect/token \
  -H "Authorization: Basic cGhvdGg6L7Jl13RmfWgtkk==pOnNlY3JldA==" \
  --data "grant_type=urn:ietf:params:oauth:grant-type:uma-ticket"
```