private async Task <bool> InvokeTokenEndpointAsync()
{
if (!string.Equals(Request.Method, "POST", StringComparison.OrdinalIgnoreCase))
{
Logger.LogError("The token request was rejected because an invalid " +
"HTTP method was received: {Method}.", Request.Method);
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "A malformed token request has been received: make sure to use POST."
}));
}
// See http://openid.net/specs/openid-connect-core-1_0.html#FormSerialization
if (string.IsNullOrEmpty(Request.ContentType))
{
Logger.LogError("The token request was rejected because the " +
"mandatory 'Content-Type' header was missing.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "A malformed token request has been received: " +
"the mandatory 'Content-Type' header was missing from the POST request."
}));
}
// May have media/type; charset=utf-8, allow partial match.
if (!Request.ContentType.StartsWith("application/x-www-form-urlencoded", StringComparison.OrdinalIgnoreCase))
{
Logger.LogError("The token request was rejected because an invalid 'Content-Type' " +
"header was received: {ContentType}.", Request.ContentType);
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "A malformed token request has been received: " +
"the 'Content-Type' header contained an unexcepted value. " +
"Make sure to use 'application/x-www-form-urlencoded'."
}));
}
var form = await Request.ReadFormAsync(Context.RequestAborted);
var request = new OpenIdConnectMessage(form.ToDictionary())
{
RequestType = OpenIdConnectRequestType.TokenRequest
};
// Store the token request in the ASP.NET context.
Context.SetOpenIdConnectRequest(request);
// Reject token requests missing the mandatory grant_type parameter.
if (string.IsNullOrEmpty(request.GrantType))
{
Logger.LogError("The token request was rejected because the grant type was missing.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "The mandatory 'grant_type' parameter was missing.",
}));
}
// Reject grant_type=authorization_code requests missing the authorization code.
// See https://tools.ietf.org/html/rfc6749#section-4.1.3
else if (request.IsAuthorizationCodeGrantType() && string.IsNullOrEmpty(request.Code))
{
Logger.LogError("The token request was rejected because the authorization code was missing.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "The mandatory 'code' parameter was missing."
}));
}
// Reject grant_type=refresh_token requests missing the refresh token.
// See https://tools.ietf.org/html/rfc6749#section-6
else if (request.IsRefreshTokenGrantType() && string.IsNullOrEmpty(request.RefreshToken))
{
Logger.LogError("The token request was rejected because the refresh token was missing.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "The mandatory 'refresh_token' parameter was missing."
}));
}
// Reject grant_type=password requests missing username or password.
// See https://tools.ietf.org/html/rfc6749#section-4.3.2
else if (request.IsPasswordGrantType() && (string.IsNullOrEmpty(request.Username) ||
string.IsNullOrEmpty(request.Password)))
{
Logger.LogError("The token request was rejected because the resource owner credentials were missing.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "The mandatory 'username' and/or 'password' parameters " +
"was/were missing from the request message."
}));
}
// When client_id and client_secret are both null, try to extract them from the Authorization header.
// See http://tools.ietf.org/html/rfc6749#section-2.3.1 and
// http://openid.net/specs/openid-connect-core-1_0.html#ClientAuthentication
if (string.IsNullOrEmpty(request.ClientId) && string.IsNullOrEmpty(request.ClientSecret))
{
string header = Request.Headers[HeaderNames.Authorization];
if (!string.IsNullOrEmpty(header) && header.StartsWith("Basic ", StringComparison.OrdinalIgnoreCase))
{
try {
var value = header.Substring("Basic ".Length).Trim();
var data = Encoding.UTF8.GetString(Convert.FromBase64String(value));
var index = data.IndexOf(':');
if (index >= 0)
{
request.ClientId = data.Substring(0, index);
request.ClientSecret = data.Substring(index + 1);
}
}
catch (FormatException) { }
catch (ArgumentException) { }
}
}
var validatingContext = new ValidateTokenRequestContext(Context, Options, request);
await Options.Provider.ValidateTokenRequest(validatingContext);
if (validatingContext.IsRejected)
{
Logger.LogInformation("The token request was rejected by application code.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = validatingContext.Error ?? OpenIdConnectConstants.Errors.InvalidClient,
ErrorDescription = validatingContext.ErrorDescription,
ErrorUri = validatingContext.ErrorUri
}));
}
// Reject grant_type=client_credentials requests if validation was skipped.
else if (validatingContext.IsSkipped && request.IsClientCredentialsGrantType())
{
Logger.LogError("The token request must be fully validated to use the client_credentials grant type.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = "Client authentication is required when using client_credentials."
}));
}
// Ensure that the client_id has been set from the ValidateTokenRequest event.
else if (validatingContext.IsValidated && string.IsNullOrEmpty(request.ClientId))
{
Logger.LogError("The token request was validated but the client_id was not set.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.ServerError,
ErrorDescription = "An internal server error occurred."
}));
}
AuthenticationTicket ticket = null;
// See http://tools.ietf.org/html/rfc6749#section-4.1
// and http://tools.ietf.org/html/rfc6749#section-4.1.3 (authorization code grant).
// See http://tools.ietf.org/html/rfc6749#section-6 (refresh token grant).
if (request.IsAuthorizationCodeGrantType() || request.IsRefreshTokenGrantType())
{
ticket = request.IsAuthorizationCodeGrantType() ?
await DeserializeAuthorizationCodeAsync(request.Code, request) :
await DeserializeRefreshTokenAsync(request.RefreshToken, request);
if (ticket == null)
{
Logger.LogError("The token request was rejected because the " +
"authorization code or the refresh token was invalid.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = "Invalid ticket"
}));
}
if (!ticket.Properties.ExpiresUtc.HasValue ||
ticket.Properties.ExpiresUtc < Options.SystemClock.UtcNow)
{
Logger.LogError("The token request was rejected because the " +
"authorization code or the refresh token was expired.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = "Expired ticket"
}));
}
// If the client was fully authenticated when retrieving its refresh token,
// the current request must be rejected if client authentication was not enforced.
if (request.IsRefreshTokenGrantType() && !validatingContext.IsValidated && ticket.IsConfidential())
{
Logger.LogError("The token request was rejected because client authentication " +
"was required to use the confidential refresh token.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = "Client authentication is required to use this ticket"
}));
}
// Note: presenters may be empty during a grant_type=refresh_token request if the refresh token
// was issued to a public client but cannot be null for an authorization code grant request.
var presenters = ticket.GetPresenters();
if (request.IsAuthorizationCodeGrantType() && !presenters.Any())
{
Logger.LogError("The token request was rejected because the authorization " +
"code didn't contain any valid presenter.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.ServerError,
ErrorDescription = "An internal server error occurred."
}));
}
// At this stage, client_id cannot be null for grant_type=authorization_code requests,
// as it must either be set in the ValidateClientAuthentication notification
// by the developer or manually flowed by non-confidential client applications.
// See https://tools.ietf.org/html/rfc6749#section-4.1.3
if (request.IsAuthorizationCodeGrantType() && string.IsNullOrEmpty(request.ClientId))
{
Logger.LogError("The token request was rejected because the mandatory 'client_id' was missing.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "client_id was missing from the token request"
}));
}
// Ensure the authorization code/refresh token was issued to the client application making the token request.
// Note: when using the refresh token grant, client_id is optional but must validated if present.
// As a consequence, this check doesn't depend on the actual status of client authentication.
// See https://tools.ietf.org/html/rfc6749#section-6
// and http://openid.net/specs/openid-connect-core-1_0.html#RefreshingAccessToken
if (!string.IsNullOrEmpty(request.ClientId) && presenters.Any() &&
!presenters.Contains(request.ClientId, StringComparer.Ordinal))
{
Logger.LogError("The token request was rejected because the authorization " +
"code was issued to a different client application.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = "Ticket does not contain matching client_id"
}));
}
// Validate the redirect_uri flowed by the client application during this token request.
// Note: for pure OAuth2 requests, redirect_uri is only mandatory if the authorization request
// contained an explicit redirect_uri. OpenID Connect requests MUST include a redirect_uri
// but the specifications allow proceeding the token request without returning an error
// if the authorization request didn't contain an explicit redirect_uri.
// See https://tools.ietf.org/html/rfc6749#section-4.1.3
// and http://openid.net/specs/openid-connect-core-1_0.html#TokenRequestValidation
var address = ticket.GetProperty(OpenIdConnectConstants.Properties.RedirectUri);
if (request.IsAuthorizationCodeGrantType() && !string.IsNullOrEmpty(address))
{
ticket.Properties.Items.Remove(OpenIdConnectConstants.Properties.RedirectUri);
if (string.IsNullOrEmpty(request.RedirectUri))
{
Logger.LogError("The token request was rejected because the mandatory 'redirect_uri' " +
"parameter was missing from the grant_type=authorization_code request.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidRequest,
ErrorDescription = "redirect_uri was missing from the token request"
}));
}
else if (!string.Equals(address, request.RedirectUri, StringComparison.Ordinal))
{
Logger.LogError("The token request was rejected because the 'redirect_uri' " +
"parameter didn't correspond to the expected value.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = "Authorization code does not contain matching redirect_uri"
}));
}
}
if (!string.IsNullOrEmpty(request.Scope))
{
// When an explicit scope parameter has been included in the token request
// but was missing from the authorization request, the request MUST be rejected.
// See http://tools.ietf.org/html/rfc6749#section-6
var scopes = ticket.GetScopes();
if (!scopes.Any())
{
Logger.LogError("The token request was rejected because the 'scope' parameter was not allowed.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = "Token request cannot contain a scope parameter" +
"if the authorization request didn't contain one"
}));
}
// When an explicit scope parameter has been included in the token request,
// the authorization server MUST ensure that it doesn't contain scopes
// that were not allowed during the authorization request.
// See https://tools.ietf.org/html/rfc6749#section-6
else if (!new HashSet <string>(scopes).IsSupersetOf(request.GetScopes()))
{
Logger.LogError("The token request was rejected because the 'scope' parameter was not valid.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = "Token request doesn't contain a valid scope parameter"
}));
}
// Replace the scopes initially granted by the scopes
// listed by the client application in the token request.
ticket.SetScopes(request.GetScopes());
}
if (request.IsAuthorizationCodeGrantType())
{
// Note: the authentication ticket is copied to avoid modifying the properties of the authorization code.
var context = new GrantAuthorizationCodeContext(Context, Options, request, ticket.Copy());
await Options.Provider.GrantAuthorizationCode(context);
if (!context.IsValidated)
{
// Note: use invalid_grant as the default error if none has been explicitly provided.
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = context.Error ?? OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = context.ErrorDescription,
ErrorUri = context.ErrorUri
}));
}
// By default, when using the authorization code grant, the authentication ticket extracted from the
// authorization code is used as-is. To avoid aligning the expiration date of the generated tokens
// with the lifetime of the authorization code, the ticket properties are automatically reset to null.
if (context.Ticket.Properties.IssuedUtc == ticket.Properties.IssuedUtc)
{
context.Ticket.Properties.IssuedUtc = null;
}
if (context.Ticket.Properties.ExpiresUtc == ticket.Properties.ExpiresUtc)
{
context.Ticket.Properties.ExpiresUtc = null;
}
ticket = context.Ticket;
}
else
{
// Note: the authentication ticket is copied to avoid modifying the properties of the refresh token.
var context = new GrantRefreshTokenContext(Context, Options, request, ticket.Copy());
await Options.Provider.GrantRefreshToken(context);
if (!context.IsValidated)
{
// Note: use invalid_grant as the default error if none has been explicitly provided.
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = context.Error ?? OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = context.ErrorDescription,
ErrorUri = context.ErrorUri
}));
}
// By default, when using the refresh token grant, the authentication ticket extracted from the
// refresh token is used as-is. To avoid aligning the expiration date of the generated tokens
// with the lifetime of the refresh token, the ticket properties are automatically reset to null.
if (context.Ticket.Properties.IssuedUtc == ticket.Properties.IssuedUtc)
{
context.Ticket.Properties.IssuedUtc = null;
}
if (context.Ticket.Properties.ExpiresUtc == ticket.Properties.ExpiresUtc)
{
context.Ticket.Properties.ExpiresUtc = null;
}
ticket = context.Ticket;
}
}
// See http://tools.ietf.org/html/rfc6749#section-4.3
// and http://tools.ietf.org/html/rfc6749#section-4.3.2
else if (request.IsPasswordGrantType())
{
var context = new GrantResourceOwnerCredentialsContext(Context, Options, request);
await Options.Provider.GrantResourceOwnerCredentials(context);
if (!context.IsValidated)
{
// Note: use invalid_grant as the default error if none has been explicitly provided.
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = context.Error ?? OpenIdConnectConstants.Errors.InvalidGrant,
ErrorDescription = context.ErrorDescription,
ErrorUri = context.ErrorUri
}));
}
ticket = context.Ticket;
}
// See http://tools.ietf.org/html/rfc6749#section-4.4
// and http://tools.ietf.org/html/rfc6749#section-4.4.2
else if (request.IsClientCredentialsGrantType())
{
var context = new GrantClientCredentialsContext(Context, Options, request);
await Options.Provider.GrantClientCredentials(context);
if (!context.IsValidated)
{
// Note: use unauthorized_client as the default error if none has been explicitly provided.
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = context.Error ?? OpenIdConnectConstants.Errors.UnauthorizedClient,
ErrorDescription = context.ErrorDescription,
ErrorUri = context.ErrorUri
}));
}
ticket = context.Ticket;
}
// See http://tools.ietf.org/html/rfc6749#section-8.3
else
{
var context = new GrantCustomExtensionContext(Context, Options, request);
await Options.Provider.GrantCustomExtension(context);
if (!context.IsValidated)
{
// Note: use unsupported_grant_type as the default error if none has been explicitly provided.
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = context.Error ?? OpenIdConnectConstants.Errors.UnsupportedGrantType,
ErrorDescription = context.ErrorDescription,
ErrorUri = context.ErrorUri
}));
}
ticket = context.Ticket;
}
var notification = new HandleTokenRequestContext(Context, Options, request, ticket);
await Options.Provider.HandleTokenRequest(notification);
if (notification.HandledResponse)
{
return(true);
}
else if (notification.Skipped)
{
return(false);
}
// Flow the changes made to the ticket.
ticket = notification.Ticket;
// Ensure an authentication ticket has been provided:
// a null ticket MUST result in an internal server error.
if (ticket == null)
{
Logger.LogError("The token request was rejected because no authentication " +
"ticket was returned by application code.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.ServerError
}));
}
if (validatingContext.IsValidated)
{
// Store a boolean indicating whether the ticket should be marked as confidential.
ticket.Properties.Items[OpenIdConnectConstants.Properties.Confidential] = "true";
}
// Always include the "openid" scope when the developer doesn't explicitly call SetScopes.
// Note: the application is allowed to specify a different "scopes": in this case,
// don't replace the "scopes" property stored in the authentication ticket.
if (!ticket.Properties.Items.ContainsKey(OpenIdConnectConstants.Properties.Scopes) &&
request.HasScope(OpenIdConnectConstants.Scopes.OpenId))
{
ticket.Properties.Items[OpenIdConnectConstants.Properties.Scopes] = OpenIdConnectConstants.Scopes.OpenId;
}
string audiences;
// When a "resources" property cannot be found in the authentication properties, infer it from the "audiences" property.
if (!ticket.Properties.Items.ContainsKey(OpenIdConnectConstants.Properties.Resources) &&
ticket.Properties.Items.TryGetValue(OpenIdConnectConstants.Properties.Audiences, out audiences))
{
ticket.Properties.Items[OpenIdConnectConstants.Properties.Resources] = audiences;
}
var response = new OpenIdConnectMessage();
// Note: by default, an access token is always returned, but the client application can use the "response_type" parameter
// to only include specific types of tokens. When this parameter is missing, an access token is always generated.
if (string.IsNullOrEmpty(request.ResponseType) || request.HasResponseType(OpenIdConnectConstants.ResponseTypes.Token))
{
// Make sure to create a copy of the authentication properties
// to avoid modifying the properties set on the original ticket.
var properties = ticket.Properties.Copy();
string resources;
if (!properties.Items.TryGetValue(OpenIdConnectConstants.Properties.Resources, out resources))
{
Logger.LogInformation("No explicit resource has been associated with the authentication ticket: " +
"the access token will thus be issued without any audience attached.");
}
// Note: when the "resource" parameter added to the OpenID Connect response
// is identical to the request parameter, keeping it is not necessary.
if (request.IsAuthorizationCodeGrantType() || (!string.IsNullOrEmpty(request.Resource) &&
!string.Equals(request.Resource, resources, StringComparison.Ordinal)))
{
response.Resource = resources;
}
// Note: when the "scope" parameter added to the OpenID Connect response
// is identical to the request parameter, keeping it is not necessary.
string scopes;
properties.Items.TryGetValue(OpenIdConnectConstants.Properties.Scopes, out scopes);
if (request.IsAuthorizationCodeGrantType() || (!string.IsNullOrEmpty(request.Scope) &&
!string.Equals(request.Scope, scopes, StringComparison.Ordinal)))
{
response.Scope = scopes;
}
response.TokenType = OpenIdConnectConstants.TokenTypes.Bearer;
response.AccessToken = await SerializeAccessTokenAsync(ticket.Principal, properties, request, response);
// Ensure that an access token is issued to avoid returning an invalid response.
// See http://openid.net/specs/oauth-v2-multiple-response-types-1_0.html#Combinations
if (string.IsNullOrEmpty(response.AccessToken))
{
Logger.LogError("An error occurred during the serialization of the " +
"access token and a null value was returned.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.ServerError,
ErrorDescription = "no valid access token was issued"
}));
}
// properties.ExpiresUtc is automatically set by SerializeAccessTokenAsync but the end user
// is free to set a null value directly in the SerializeAccessToken event.
if (properties.ExpiresUtc.HasValue && properties.ExpiresUtc > Options.SystemClock.UtcNow)
{
var lifetime = properties.ExpiresUtc.Value - Options.SystemClock.UtcNow;
var expiration = (long)(lifetime.TotalSeconds + .5);
response.ExpiresIn = expiration.ToString(CultureInfo.InvariantCulture);
}
}
// Note: by default, an identity token is always returned when the "openid" scope has been requested,
// but the client application can use the "response_type" parameter to only include specific types of tokens.
// When this parameter is missing, an identity token is always generated.
if (ticket.HasScope(OpenIdConnectConstants.Scopes.OpenId) &&
(string.IsNullOrEmpty(request.ResponseType) || request.HasResponseType(OpenIdConnectConstants.ResponseTypes.IdToken)))
{
// Make sure to create a copy of the authentication properties
// to avoid modifying the properties set on the original ticket.
var properties = ticket.Properties.Copy();
response.IdToken = await SerializeIdentityTokenAsync(ticket.Principal, properties, request, response);
// Ensure that an identity token is issued to avoid returning an invalid response.
// See http://openid.net/specs/openid-connect-core-1_0.html#TokenResponse
// and http://openid.net/specs/openid-connect-core-1_0.html#RefreshTokenResponse
if (string.IsNullOrEmpty(response.IdToken))
{
Logger.LogError("An error occurred during the serialization of the " +
"identity token and a null value was returned.");
return(await SendErrorPayloadAsync(new OpenIdConnectMessage {
Error = OpenIdConnectConstants.Errors.ServerError,
ErrorDescription = "no valid identity token was issued"
}));
}
}
// Note: by default, a refresh token is always returned when the "offline_access" scope has been requested,
// but the client application can use the "response_type" parameter to only include specific types of tokens.
// When this parameter is missing, a refresh token is always generated.
if (ticket.HasScope(OpenIdConnectConstants.Scopes.OfflineAccess) &&
(!request.IsRefreshTokenGrantType() || Options.UseSlidingExpiration) &&
(string.IsNullOrEmpty(request.ResponseType) || request.HasResponseType(OpenIdConnectConstants.Parameters.RefreshToken)))
{
// Make sure to create a copy of the authentication properties
// to avoid modifying the properties set on the original ticket.
var properties = ticket.Properties.Copy();
response.RefreshToken = await SerializeRefreshTokenAsync(ticket.Principal, properties, request, response);
}
var payload = new JObject();
foreach (var parameter in response.Parameters)
{
payload.Add(parameter.Key, parameter.Value);
}
var responseNotification = new ApplyTokenResponseContext(Context, Options, ticket, request, payload);
await Options.Provider.ApplyTokenResponse(responseNotification);
if (responseNotification.HandledResponse)
{
return(true);
}
else if (responseNotification.Skipped)
{
return(false);
}
using (var buffer = new MemoryStream())
using (var writer = new JsonTextWriter(new StreamWriter(buffer))) {
payload.WriteTo(writer);
writer.Flush();
Response.ContentLength = buffer.Length;
Response.ContentType = "application/json;charset=UTF-8";
Response.Headers[HeaderNames.CacheControl] = "no-cache";
Response.Headers[HeaderNames.Pragma] = "no-cache";
Response.Headers[HeaderNames.Expires] = "-1";
buffer.Seek(offset: 0, loc: SeekOrigin.Begin);
await buffer.CopyToAsync(Response.Body, 4096, Context.RequestAborted);
return(true);
}
}
/// <summary> /// Called when a request to the Token endpoint arrives with a "grant_type" of "client_credentials". This occurs when a registered client /// application wishes to acquire an "access_token" to interact with protected resources on it's own behalf, rather than on behalf of an authenticated user. /// If the web application supports the client credentials it may assume the context.ClientId has been validated by the ValidateClientAuthentication call. /// To issue an access token the context.Validated must be called with a new ticket containing the claims about the client application which should be associated /// with the access token. The application should take appropriate measures to ensure that the endpoint isn't abused by malicious callers. /// The default behavior is to reject this grant type. /// See also http://tools.ietf.org/html/rfc6749#section-4.4.2 /// </summary> /// <param name="context">The context of the event carries information in and results out.</param> /// <returns>Task to enable asynchronous execution</returns> public virtual Task GrantClientCredentials(GrantClientCredentialsContext context) => OnGrantClientCredentials(context);