Add mapping for DPoP in DefaultMapOAuth2AccessTokenResponseConverter

[hammadirshad]

This PR adds the missing mapping for the newly introduced TokenType.DPOP in DefaultMapOAuth2AccessTokenResponseConverter. Without this mapping, deserializing an OAuth 2.0 Access Token Response containing a DPoP token type results in an error:
An error occurred reading the OAuth 2.0 Access Token Response: tokenType cannot be null

Stacktrace

org.springframework.web.client.RestClientException: Error while extracting response for type [org.springframework.security.oauth2.core.endpoint.OAuth2AccessTokenResponse] and content type [application/json;charset=UTF-8]
	at org.springframework.web.client.DefaultRestClient.readWithMessageConverters(DefaultRestClient.java:261) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.readBody(DefaultRestClient.java:814) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.lambda$body$0(DefaultRestClient.java:745) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.web.client.DefaultRestClient$DefaultRequestBodyUriSpec.exchangeInternal(DefaultRestClient.java:574) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.web.client.DefaultRestClient$DefaultRequestBodyUriSpec.exchange(DefaultRestClient.java:535) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.web.client.RestClient$RequestHeadersSpec.exchange(RestClient.java:677) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.executeAndExtract(DefaultRestClient.java:809) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.web.client.DefaultRestClient$DefaultResponseSpec.body(DefaultRestClient.java:745) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.security.oauth2.client.endpoint.AbstractRestClientOAuth2AccessTokenResponseClient.getTokenResponse(AbstractRestClientOAuth2AccessTokenResponseClient.java:94) ~[spring-security-oauth2-client-6.5.0-M3.jar:6.5.0-M3]
	... 25 common frames omitted
Caused by: org.springframework.http.converter.HttpMessageNotReadableException: An error occurred reading the OAuth 2.0 Access Token Response: tokenType cannot be null
	at org.springframework.security.oauth2.core.http.converter.OAuth2AccessTokenResponseHttpMessageConverter.readInternal(OAuth2AccessTokenResponseHttpMessageConverter.java:81) ~[spring-security-oauth2-core-6.5.0-M3.jar:6.5.0-M3]
	at org.springframework.security.oauth2.core.http.converter.OAuth2AccessTokenResponseHttpMessageConverter.readInternal(OAuth2AccessTokenResponseHttpMessageConverter.java:47) ~[spring-security-oauth2-core-6.5.0-M3.jar:6.5.0-M3]
	at org.springframework.http.converter.AbstractHttpMessageConverter.read(AbstractHttpMessageConverter.java:198) ~[spring-web-6.2.5.jar:6.2.5]
	at org.springframework.web.client.DefaultRestClient.readWithMessageConverters(DefaultRestClient.java:244) ~[spring-web-6.2.5.jar:6.2.5]
	... 33 common frames omitted
Caused by: java.lang.IllegalArgumentException: tokenType cannot be null
	at org.springframework.util.Assert.notNull(Assert.java:181) ~[spring-core-6.2.5.jar:6.2.5]
	at org.springframework.security.oauth2.core.OAuth2AccessToken.<init>(OAuth2AccessToken.java:76) ~[spring-security-oauth2-core-6.5.0-M3.jar:6.5.0-M3]
	at org.springframework.security.oauth2.core.endpoint.OAuth2AccessTokenResponse$Builder.build(OAuth2AccessTokenResponse.java:191) ~[spring-security-oauth2-core-6.5.0-M3.jar:na]
	at org.springframework.security.oauth2.core.endpoint.DefaultMapOAuth2AccessTokenResponseConverter.convert(DefaultMapOAuth2AccessTokenResponseConverter.java:64) ~[classes/:na]
	at org.springframework.security.oauth2.core.endpoint.DefaultMapOAuth2AccessTokenResponseConverter.convert(DefaultMapOAuth2AccessTokenResponseConverter.java:37) ~[classes/:na]
	at org.springframework.security.oauth2.core.http.converter.OAuth2AccessTokenResponseHttpMessageConverter.readInternal(OAuth2AccessTokenResponseHttpMessageConverter.java:77) ~[spring-security-oauth2-core-6.5.0-M3.jar:6.5.0-M3]
	... 36 common frames omitted

[jgrandja]

@hammadirshad

The Spring team recently migrated to the Developer Certificate of Origin (DCO) for our contribution process. See Submitting Pull Requests for additional details on the new process. Please format the commit in this PR as the DCO check did not pass.

The changes look good in the PR so we'll get this merged as soon as the DCO check passes. However, please update the copyright year in the 2 files. Thank you.

[hammadirshad]

Hi @jgrandja
I have updated the copyright year and added Signed-off-by for DCO check.

[jgrandja]

Thanks for the update @hammadirshad. This is now merged.