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This module contains client library for Microsoft Azure Identity.
There is a newer version: 1.16.0-beta.1
// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

package com.azure.identity;

import com.azure.core.annotation.Immutable;
import com.azure.core.credential.AccessToken;
import com.azure.core.credential.TokenCredential;
import com.azure.core.credential.TokenRequestContext;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.util.ArrayList;
import java.util.Deque;
import java.util.List;
import java.util.stream.Collectors;

/**
 * A token credential provider that can provide a credential from a list of providers.
 *
 * Sample: Construct a ChainedTokenCredential with silent username+password login tried first, then
 * interactive browser login as needed (e.g. when 2FA is turned on in the directory).
 *  * UsernamePasswordCredential usernamePasswordCredential = new UsernamePasswordCredentialBuilder()
 *     .clientId(clientId)
 *     .username(username)
 *     .password(password)
 *     .build();
 * InteractiveBrowserCredential interactiveBrowserCredential = new InteractiveBrowserCredentialBuilder()
 *     .clientId(clientId)
 *     .port(8765)
 *     .build();
 * ChainedTokenCredential credential = new ChainedTokenCredentialBuilder()
 *     .addLast(usernamePasswordCredential)
 *     .addLast(interactiveBrowserCredential)
 *     .build();
 * 
 */
@Immutable
public class ChainedTokenCredential implements TokenCredential {
    private final Deque credentials;

    /**
     * Create an instance of chained token credential that aggregates a list of token
     * credentials.
     */
    ChainedTokenCredential(Deque credentials) {
        this.credentials = credentials;
    }

    @Override
    public Mono getToken(TokenRequestContext request) {
        List exceptions = new ArrayList<>(4);
        return Flux.fromIterable(credentials)
                   .flatMap(p -> p.getToken(request).onErrorResume(CredentialUnavailableException.class, t -> {
                       exceptions.add(t);
                       return Mono.empty();
                   }), 1)
                   .next()
                   .switchIfEmpty(Mono.defer(() -> {

                       StringBuilder message = new StringBuilder("Tried "
                             + credentials.stream().map(c -> c.getClass().getSimpleName())
                                   .collect(Collectors.joining(", "))
                             + " but failed to acquire a token for any of them. Please verify the"
                             + " environment for the credentials"
                             + " and see more details in the causes below.");

                       // Chain Exceptions.
                       CredentialUnavailableException last = exceptions.get(exceptions.size() - 1);
                       for (int z = exceptions.size() - 2; z >= 0; z--) {
                           CredentialUnavailableException current = exceptions.get(z);
                           last = new CredentialUnavailableException(current.getMessage(), last);
                       }
                       return Mono.error(new CredentialUnavailableException(message.toString(), last));
                   }));
    }
}