oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/web/server/WebSessionOAuth2ServerAuthorizationRequestRepository.java
private String getStateParameter(ServerWebExchange exchange) {
		Assert.notNull(exchange, "exchange cannot be null");
		return exchange.getRequest().getQueryParams().getFirst(OAuth2ParameterNames.STATE);
	}
private String getStateParameter(ServerWebExchange exchange) {
		Assert.notNull(exchange, "exchange cannot be null");
		return exchange.getRequest().getQueryParams().getFirst(OAuth2ParameterNames.STATE);
	}
Gets the state parameter from the {@link ServerHttpRequest}
@param exchange the exchange to use
@return the state parameter or null if not found