feat(pnv): Add support for Firebase Phone Number Verification

AGENTS.md

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+# AI coding assistant guidelines: Firebase Admin Java SDK
+
+This document defines repository-wide expectations, code styles, and Checkstyle compliance metrics that every autonomous AI coding agent or pair programming assistant must strictly follow when introducing or modifying code in this repository.
+
+---
+
+## 🎨 Code Style & Checkstyle Compliance
+
+This repository enforces standard **Google Java Style** guidelines validated through automated Maven checkstyle executions (`checkstyle.xml`). Any compilation or pull request build will fail if these constraints are violated.
+
+### 1. Strict 100-Character Line Limit
+*   **Rule:** No line of code, comments, Javadoc documentation entries, or inline string literal concatenations may exceed **100 characters** under any circumstances.
+*   **Remediation:** 
+    *   Break long method parameters, array initializations, and logic comparisons onto separate lines.
+    *   Wrap long `assertThrows` statements or lambda chains across multiple contiguous lines.
+    *   Format long log messages, exception messages, or assertion string explanations using standard string block concatenation broken across separate lines.
+
+### 2. Import Ordering & Grouping
+*   **Rule:** Imports must be grouped and arranged alphabetically to avoid validation noise.
+*   **Remediation:** 
+    1.  Static imports placed first, grouped, and alphabetically arranged.
+    2.  Non-static imports grouped alphabetically by package tier.
+    3.  Avoid utilizing wildcard (`*`) imports. Every import declaration must be explicit.
+
+### 3. Javadoc Completeness & Formatting
+*   **Rule:** Every public class, package-private component interface, constructor, and public method signature must include fully formed Javadoc documentation blocks.
+*   **Remediation:** 
+    *   Document all arguments via `@param`, explain error flows via `@throws`, and clear return constraints via `@return`.
+    *   Wrap documentation description text explicitly so that no single javadoc documentation line passes the 100 characters limit.
+
+### 4. Indentation & Spacing
+*   **Rule:** Standard indentation uses exactly **2 spaces** per block indentation level. **4 spaces** are used explicitly for wrapped line continuation indentation.
+*   **Remediation:** Never utilize tab characters. Ensure block braces follow the Google K&R opening line placement convention.

pom.xml

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             <artifactId>httpclient5</artifactId>
             <version>5.3.1</version>
         </dependency>
+        <dependency>
+            <groupId>com.nimbusds</groupId>
+            <artifactId>nimbus-jose-jwt</artifactId>
+            <version>10.6</version>
+        </dependency>
 
         <!-- Test Dependencies -->
         <dependency>

src/main/java/com/google/firebase/phonenumberverification/FirebasePhoneNumberVerification.java

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+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.phonenumberverification;
+
+import com.google.firebase.FirebaseApp;
+import com.google.firebase.ImplFirebaseTrampolines;
+import com.google.firebase.internal.FirebaseService;
+import com.google.firebase.phonenumberverification.internal.FirebasePhoneNumberVerificationTokenVerifier;
+
+/**
+ * This class is the entry point for the Firebase Phone Number Verification service.
+ *
+ * <p>You can get an instance of {@link FirebasePhoneNumberVerification} via {@link #getInstance()},
+ * or {@link #getInstance(FirebaseApp)} and then use it.
+ */
+public final class FirebasePhoneNumberVerification {
+  private static final String SERVICE_ID = FirebasePhoneNumberVerification.class.getName();
+  private final FirebasePhoneNumberVerificationTokenVerifier tokenVerifier;
+
+  private FirebasePhoneNumberVerification(FirebaseApp app) {
+    this.tokenVerifier = new FirebasePhoneNumberVerificationTokenVerifier(app);
+  }
+
+  /**
+   * Gets the {@link FirebasePhoneNumberVerification} instance for the default {@link FirebaseApp}.
+   *
+   * @return The {@link FirebasePhoneNumberVerification} instance for the default
+   *     {@link FirebaseApp}.
+   */
+  public static FirebasePhoneNumberVerification getInstance() {
+    return getInstance(FirebaseApp.getInstance());
+  }
+
+  /**
+   * Gets the {@link FirebasePhoneNumberVerification} instance for the specified
+   * {@link FirebaseApp}.
+   *
+   * @return The {@link FirebasePhoneNumberVerification} instance for the specified
+   *     {@link FirebaseApp}.
+   */
+  public static synchronized FirebasePhoneNumberVerification getInstance(FirebaseApp app) {
+    FirebasePhoneNumberVerificationService service =
+        ImplFirebaseTrampolines.getService(app, SERVICE_ID,
+            FirebasePhoneNumberVerificationService.class);
+    if (service == null) {
+      service = ImplFirebaseTrampolines.addService(
+          app, new FirebasePhoneNumberVerificationService(app));
+    }
+    return service.getInstance();
+  }
+
+  /**
+   * Verifies a Firebase Phone Number Verification token (JWT).
+   *
+   * @param phoneNumberVerificationJwt The JWT string to verify.
+   * @return A verified {@link FirebasePhoneNumberVerificationToken}.
+   * @throws FirebasePhoneNumberVerificationException If verification fails.
+   */
+  public FirebasePhoneNumberVerificationToken verifyToken(String phoneNumberVerificationJwt)
+      throws FirebasePhoneNumberVerificationException {
+    return this.tokenVerifier.verifyToken(phoneNumberVerificationJwt);
+  }
+
+  private static class FirebasePhoneNumberVerificationService
+      extends FirebaseService<FirebasePhoneNumberVerification> {
+    FirebasePhoneNumberVerificationService(FirebaseApp app) {
+      super(SERVICE_ID, new FirebasePhoneNumberVerification(app));
+    }
+  }
+}

src/main/java/com/google/firebase/phonenumberverification/FirebasePhoneNumberVerificationErrorCode.java

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+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.phonenumberverification;
+
+/**
+ * Error codes that are used in {@link FirebasePhoneNumberVerification}.
+ */
+public enum FirebasePhoneNumberVerificationErrorCode {
+  INVALID_ARGUMENT,
+  INVALID_TOKEN,
+  TOKEN_EXPIRED,
+  INTERNAL_ERROR,
+  SERVICE_ERROR,
+}

src/main/java/com/google/firebase/phonenumberverification/FirebasePhoneNumberVerificationException.java

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+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.phonenumberverification;
+
+import com.google.firebase.ErrorCode;
+import com.google.firebase.FirebaseException;
+
+/**
+ * Generic exception related to Firebase Phone Number Verification.
+ * Check the error code and message for more details.
+ */
+public class FirebasePhoneNumberVerificationException extends FirebaseException {
+  private final FirebasePhoneNumberVerificationErrorCode errorCode;
+
+  /**
+   * Exception that created from {@link FirebasePhoneNumberVerificationErrorCode},
+   * {@link String} message and {@link Throwable} cause.
+   *
+   * @param errorCode {@link FirebasePhoneNumberVerificationErrorCode}
+   * @param message {@link String}
+   * @param cause {@link Throwable}
+   */
+  public FirebasePhoneNumberVerificationException(
+      FirebasePhoneNumberVerificationErrorCode errorCode,
+      String message,
+      Throwable cause
+  ) {
+    super(mapToFirebaseError(errorCode), message, cause);
+    this.errorCode = errorCode;
+  }
+
+  /**
+   * Exception that created from {@link FirebasePhoneNumberVerificationErrorCode}
+   * and {@link String} message.
+   *
+   * @param errorCode {@link FirebasePhoneNumberVerificationErrorCode}
+   * @param message {@link String}
+   */
+  public FirebasePhoneNumberVerificationException(
+      FirebasePhoneNumberVerificationErrorCode errorCode,
+      String message
+  ) {
+    this(errorCode, message, null);
+  }
+
+  public FirebasePhoneNumberVerificationErrorCode getPhoneNumberVerificationErrorCode() {
+    return errorCode;
+  }
+
+  private static ErrorCode mapToFirebaseError(FirebasePhoneNumberVerificationErrorCode code) {
+    if (code == null) {
+      return ErrorCode.INTERNAL;
+    }
+    switch (code) {
+      case INVALID_ARGUMENT:
+        return ErrorCode.INVALID_ARGUMENT;
+      case TOKEN_EXPIRED:
+      case INVALID_TOKEN:
+        return ErrorCode.UNAUTHENTICATED;
+      case SERVICE_ERROR:
+        return ErrorCode.UNAVAILABLE;
+      case INTERNAL_ERROR:
+      default:
+        return ErrorCode.INTERNAL;
+    }
+  }
+}

src/main/java/com/google/firebase/phonenumberverification/FirebasePhoneNumberVerificationToken.java

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+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.phonenumberverification;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Represents a verified Firebase Phone Number Verification token.
+ */
+public class FirebasePhoneNumberVerificationToken {
+  private final Map<String, Object> claims;
+
+  /**
+   * Create an instance of {@link FirebasePhoneNumberVerificationToken} from a map of JWT claims.
+   *
+   * @param claims A map of JWT claims.
+   */
+  public FirebasePhoneNumberVerificationToken(Map<String, Object> claims) {
+    checkNotNull(claims, "Claims map must not be null");
+    checkArgument(claims.containsKey("sub"), "Claims map must contain sub");
+    this.claims = ImmutableMap.copyOf(claims);
+  }
+
+  /**
+   * Returns the issuer identifier for the issuer of the response.
+   */
+  public String getIssuer() {
+    return (String) claims.get("iss");
+  }
+
+  /**
+   * Returns the phone number of the user.
+   * This corresponds to the 'sub' claim in the JWT.
+   */
+  public String getPhoneNumber() {
+    return (String) claims.get("sub");
+  }
+
+  /**
+   * Returns the audience for which this token is intended.
+   */
+  public List<String> getAudience() {
+    Object audience = claims.get("aud");
+    if (audience instanceof String) {
+      return ImmutableList.of((String) audience);
+    } else if (audience instanceof List) {
+      @SuppressWarnings("unchecked")
+      List<String> audienceList = (List<String>) audience;
+      return ImmutableList.copyOf(audienceList);
+    }
+    return ImmutableList.of();
+  }
+
+  /**
+   * Returns the expiration time in seconds since the Unix epoch.
+   */
+  public long getExpirationTime() {
+    Object exp = claims.get("exp");
+    if (exp instanceof java.util.Date) {
+      return ((java.util.Date) exp).getTime() / 1000L;
+    }
+    return exp instanceof Number ? ((Number) exp).longValue() : 0L;
+  }
+
+  /**
+   * Returns the issued-at time in seconds since the Unix epoch.
+   */
+  public long getIssuedAt() {
+    Object iat = claims.get("iat");
+    if (iat instanceof java.util.Date) {
+      return ((java.util.Date) iat).getTime() / 1000L;
+    }
+    return iat instanceof Number ? ((Number) iat).longValue() : 0L;
+  }
+
+  /**
+   * Returns the entire map of claims.
+   */
+  public Map<String, Object> getClaims() {
+    return claims;
+  }
+}